Pumpkin Spice Custard Buns

These buns are a twist on the classic Chinese egg custard buns (奶黃包, nǎihuángbāo). They still have the creamy custard and the fluffy steamed bun, but I added pumpkin and fall spices to both the filling and the dough to create a pumpkin spice version. Notes on ingredient substitutions and the science behind the custard filling, dough, and steaming process follow the recipe. I also made these in a video over on YouTube!

Pumpkin Spice Steamed Buns

Makes 12 buns

奶黃包 egg custard buns are reimagined for fall with pumpkin purée and a hint of warm fall spices. These buns are perfect for breakfast or a quick snack! Follow the make-ahead tips to have them ready for a holiday meal. The best part? They won’t even take up oven space.

Ingredients

Thinking about making substitutions? Check the notes after the recipe!

Custard filling

  • 32g (1/4 c) cornstarch
  • 72g (1/3 c) brown sugar, divided
  • 2 large eggs
  • 320g (320 mL, 1-1/3 c) whole milk
  • 244g (1 cup) pumpkin purée, fresh or canned
  • 1/2 tsp cinnamon
  • 1/4 tsp ginger
  • 1/4 tsp nutmeg
  • 1/16 tsp freshly ground black pepper
  • 1/8 tsp salt

Dough

  • 300g (about 2-1/4 c + 2 Tbsp, spooned and leveled) all-purpose flour
  • 50g (6 Tbsp) cornstarch
  • 1-1/4 tsp instant yeast (about half a packet)
  • 65g (about 1/4 c + 1 Tbsp) brown sugar
  • 1/4 tsp cinnamon
  • 240g (1 cup) pumpkin purée, fresh or canned, microwaved for about 1 minute until lukewarm

Method

  1. To make the custard, whisk the cornstarch and half the sugar (36g) together in a heat-proof bowl. In a second bowl, lightly beat the eggs.
  2. Combine the milk and remaining sugar (36g) in a saucepan. Heat the mixture over medium heat, stirring occasionally until the sugar dissolves and the milk begins to bubble at the edges.
  3. Whisk the eggs into the cornstarch mixture. Slowly pour the hot milk into the egg mixture, whisking constantly. Once all of the milk is whisked into the egg, pour this mixture back into the saucepan and return to medium-low heat, stirring constantly until the mixture thickens, about 3–5 minutes. The custard will be very thick, like the consistency of choux paste.
  4. Remove custard from heat and whisk in the pumpkin purée, spices, and salt. Set aside to cool to room temperature.
  5. In the meantime, prepare the dough. Whisk all of the dough ingredients except the pumpkin purée in a large bowl. Add the pumpkin and knead into a dough. Depending on the amount of water in your purée, you may need to add flour or water to form a stiff dough. Knead the dough until smooth, about 5–10 minutes depending on your strength and technique. Cover and rest for 15–20 min. The dough may not have risen noticeably; that is fine.
  6. Divide the dough into 12, shape each portion into a smooth ball by tucking the edges to the bottom, cover, and rest again for 15–20 min. After resting, roll each piece into a disk about 5 inches (13 cm) across, add 40–45g (2 Tbsp) custard to the center, and pinch the edges together in the center. Place bun seam-side down on a square of parchment. Keep any dough or buns covered when you’re not actively working with them.
  7. Cover the buns and let them rise until they’ve increased in volume by about half. Depending on the conditions of your kitchen, this may take 15 minutes or an hour. To speed up the process, make sure the dough is in a warm spot.
  8. Fill a pan with cold water, place the buns inside on a plate or steamer, and cover with the lid. Turn the heat on high and bring the water to a rolling boil. Turn the heat down if you like, but make sure the intensity of the boil does not decrease, and continue boiling for 15 more minutes. If you need to separate the buns into more than two batches, cover and refrigerate the raw buns so they don’t overproof and add 1 minute to their steaming time.
  9. Remove buns from steamer and serve warm. Cooked, cooled buns can be stored in an airtight container at room temperature for 3 days. For longer storage, freeze cooked, cooled buns in an airtight container. To reheat, steam for 5 minutes from room temperature or 15 minutes from frozen. Or, cover and microwave until soft and fluffy. In my 600-watt microwave on high power, this takes about 45 seconds from room temperature or 90 seconds from frozen. The buns can become crunchy if they’re not covered or if they’re microwaved for too long, so be sure to check them frequently the first time.

Make ahead

  1. Make the custard up to 2 days in advance. After it cools, cover with plastic wrap and keep refrigerated until use. Note that the custard will firm and weep over time because of the cornstarch. You can learn more about that process here.
  2. Make the dough 1 day in advance. After kneading the dough, cover and refrigerate up to 1 day. When you’re ready to use it, punch it down and knead it briefly, and proceed with the recipe as written. The rise in Step 7 may take longer because the dough is cold.
  3. Store the steamed buns at room temperature or in the freezer and reheat in the microwave as described in Step 9 of the recipe.

Substitutions

Vegan: The milk can be substituted with a plant-based milk, though the flavor of the pumpkin custard may change. You may also omit the egg, though you may need to add a little cornstarch to compensate and the filling may not be as rich. Simply whisk all the cornstarch and sugar into the milk and cook until thickened.

Whole milk: The milk provides the liquid for the custard. Any type of dairy or non-dairy milk (or even water) should work here, but keep in mind the flavor and richness of the custard will change.

Pumpkin purée: I tested this recipe using fresh roasted pumpkin purée. I’ve also used butternut squash, which works just as well and has an even brighter orange color. You could probably swap other similar squashes as well. Depending on the water content of your purée, which may vary based on the type of squash and the cooking method, you may need to adjust the ingredient ratios to obtain the right consistency. Roasted squash, for example, tends to be drier than steamed or microwaved squash. Add flour to firm up the dough, and add purée or water to soften it. Make adjustments gradually and be sure to fully incorporate the extra flour or liquid before adding more. A dough that is too wet will not hold its shape well, and the bun will flatten as it proofs.

Spices: Trust me on the black pepper! You can’t taste it in the custard, but it adds another level of warmth. Sally’s Baking Addiction uses it in her pumpkin pie. Also, feel free to use 1 tsp of your favorite pumpkin pie spice blend for the custard. If you prefer a stronger pumpkin pie taste, you may also increase the amount of spice in the custard.

Brown sugar: I prefer the flavor of brown sugar, but granulated sugar will work in a pinch.

Custard science

The custard filling for these buns is thickened by egg and cornstarch. For a refresher on the science of starches, you can check out the chemical structure of starches and how they thicken custards. You can also watch me explain custard science in the video below!

No scrambled eggs

One of the most nerve-wracking parts of making any custard is heating the eggs. But we have to heat the egg proteins into the correct shape to set the custard. So we ask for the mercy of the Custard Powers even as we marshal all of our techniques to prevent the eggs from scrambling.

In a raw egg, long strings of protein are coiled into individual balls. Remember that proteins are strings of amino acid beads, and some beads stick together to fold the protein string into a three-dimensional shape. Raw egg white is translucent because light can pass through the spaces between the balled-up proteins. But these proteins simply float in our custard mixture without adding any structure, so an uncooked custard is just a soupy mess.

Proteins are strings of amino acid beads. Rules about bead interactions fold the protein string into a three-dimensional shape.

When we heat an egg, we pull apart amino acid beads and the protein strings unravel. But the beads still want to stick to a buddy. So they find new partners on neighboring protein strings. When many unraveled protein strings stick together, they form the extensive structure we want in everything from fried eggs to cakes. As an egg continues to cook, the unraveled proteins draw closer and closer together. These protein aggregates block light from passing through, so the white becomes opaque.

The more we heat an egg, the closer these proteins draw. In the process, they squeeze out water from between them. An overcooked egg white is tough and rubbery because the proteins are packed so tightly together, and it’s dry because the egg has lost water. In a custard, there’s a lot of milk, so the proteins are spaced further apart. As a result, the texture of an egg custard is more tender and delicate. (This is also why a bit of milk or water can make such fluffy scrambled eggs.)

As proteins (left) cook, they unravel (center) then stick to each other (right).

In a scrambled egg custard, the egg proteins have clumped into curds floating in water. What we want instead is an even distribution of unraveled egg proteins throughout the entire custard mixture. Custards are so prone to curdling because, once unraveled, the egg protein strings really want to stick together. It takes a lot of work on our part to keep them distant, but we’ll see that most strategies either slow down the unraveling process or keep the unraveled proteins separate.

Heating the eggs

One way to prevent a custard from curdling is to temper the eggs. We drizzle hot milk into the cool eggs while whisking to increase the temperature gradually. This way, the proteins unwind slowly, giving us time to whisk them apart before they stick to each other.

The sugar in the egg also prevents the eggs from scrambling. Sugar loves water, so it draws it away from the egg proteins. Without water, the proteins have a harder time unraveling, which gives us more time to separate them. (Sugar stabilizes meringues the same way.) However, because sugar attracts water, it’s important not to whisk it into the egg too early. Otherwise, the sugar changes the texture of the egg. For this recipe, I also split half the sugar into the milk so the egg mixture wouldn’t be too thick.

Sugar molecules draw water to themselves.

The eggs are also mixed with cornstarch. Since the milk is hot, the starch will absorb liquid and swell, becoming physical obstacles that block the egg proteins from sticking together. It also adds more body to the texture of the custard. If you get all of the milk into the eggs without scrambling them, you’ve probably appeased the Custard Powers. From this point forward, the cornstarch will prevent the egg from curdling, so we can cook the custard over direct heat instead of a water bath.

Cooking the custard

When the mixture goes back on the stove, the egg proteins continue to unravel and form their protein network. We still have to stir constantly to ensure the mixture heats evenly, but we’re more worried about the cornstarch clumping as it gelatinizes and thickens. Wait for the custard thicken completely. This way, the cornstarch won’t continue to thicken the filling into a starchy mess when we steam the buns. Also, a thick custard is easier to wrap.

With heat, starch swells and gelatinizes to thicken a liquid.

It’s also important to make sure the mixture, thick as it is, bubbles a handful of times before we turn off the heat. We want to make sure we’ve cooked the custard to a temperature high enough to deactivate amylases in the egg yolks. Amylases are enzymes that attack starch. If we don’t deactivate them, they will break down the gelatinized cornstarch and thin the custard.

After we remove the mixture from the heat, the gelatinized starch will continue to thicken the custard as it cools. Be sure to whisk in the pumpkin and spices while the custard is still warm. If we stir or agitate it after it cools, we disrupt the starch and the custard will thin. For me, the custard is thick enough to wrap at room temperature, but you can also refrigerate it to firm it.

Large starch molecules (left) jumble together and cannot move, thickening the liquid. If these molecules are broken down (right), either by amylase or mixing, they lose their thickening ability.

Bun science

Developing the dough

I tried several iterations of the dough. I wanted a soft, fluffy bun, and I also wanted to pack as much pumpkin into the dough as I could for a brighter color. Since pumpkin purée contains moisture, I replaced all of the liquid in the dough with pumpkin. I started with a dough (Batch 1) that contained only pumpkin (65g), brown sugar (17g), flour (87g), and yeast (1/4 tsp). Although this created beautiful buns that held their shape beautifully, the texture was chewier and denser than I’d hoped, more suitable for an unfilled bun (饅頭, mántóu).

The dough on the left contained pumpkin and water, so it was paler than the dough on the right (Batch 1).

For the next batch (Batch 2), I added vegetable oil (1 tsp) to the dough. Fats like oil add tenderness to baked goods by preventing gluten from forming, and I was hoping this would soften the bun. Since the oil coats gluten proteins in the flour, I also reduced the pumpkin to compensate for decreased water absorption. I used 63g, but the dough was stickier than I intended so I added some extra flour.

At the same time, I made a third batch of dough (Batch 3) where I replaced some of the flour with cornstarch. I got the idea from the egg custard bun recipe from What to Cook Today. Cornstarch still absorbs water and contributes structure, but starch texture is considered more tender than that of gluten. And just like in the custard, the starch can prevent gluten proteins from tightening and toughening. By using less flour in the dough, we also reduce the overall amount of gluten.

Both the oil and the cornstarch softened the bun, but I preferred the texture of the cornstarch. It made a looser, fluffier bun.

As I mentioned in the substitution notes, the water content of squash purées will vary. When I make these buns, I like to add about 220g pumpkin to the dry ingredients, knead, and then add 5–10g pumpkin at a time until the dough reaches the correct firmness. As the dough comes together, make sure to knead thoroughly to assess its consistency before adding more purée. A dough that is too wet will not hold its shape, and the bun will flatten as it proofs.

Resting the dough

Notice that the recipe includes two “resting” periods in steps 5 and 6. The purpose of these periods is not for the dough to rise; rather, it is to relax the gluten. Remember that gluten is elastic, which means it springs back into shape. Without these rest periods, the dough shrinks if we try to roll it out. Every time we handle the dough, whether it’s to knead it, portion it, or roll it into discs, we realign the gluten. If we don’t give the gluten time to relax into its new orientation, the dough becomes tight and difficult to manage. You can rest any dough that’s becoming too tight to knead or shape. Just cover it and walk away for 10–20 minutes. It’ll be much easier to handle when you return.

Shaping the dough

Typically, the dough for filled buns is rolled so that the edges are thinner than the center. This way, when the edges are pinched closed, there isn’t an excessive amount of dough at the bottom of the bun. Feel free to try the method I show in the video to roll the dough, or use whichever way is easiest for you. No matter what, make sure the dough isn’t too thin, or else the custard will leak through. As far as the pleating goes, these buns are forgiving because they’re steamed seam-side down. I like the method I use in the video because I can add more filling, but do what works best for you. Just make sure that the bun is fully sealed so the custard doesn’t leak out.

Shaped buns ready to proof. The steamed versions of these are in the first photo above.

Proofing the dough

The only proofing time in this recipe is in step 7, once the buns are shaped. This gives the yeast time to produce some gases and leaven the dough for a light, fluffy bun. The length of time for this proof will depend on how happy the yeast are. To make sure this process goes quickly, make sure to warm the pumpkin before adding it to the dough, and keep the dough in a warm place. You can also read the yeast post to see other factors that influence yeast activity.

The recipe reads that the buns should gain about half their volume by the end of the proof. Notice this does not mean that the bun should have expanded by 50% in all three dimensions—that would be more than a threefold increase in volume (1.53 = 3.4). Instead, they should be noticeably poofier but not dramatically bigger. (Mathematically, it works to about a 15% increase in each dimension, but I just look for extra poof!)

Steam science

As we’ve explored here, steaming provides the buns with a wet environment that does not exceed 212°F (100°C). As a result, starch gelatinizes on the surface of the bun to create a shiny skin, and the buns don’t brown. Also, because the dough does not lose water, steamed bun doughs often contain less water than baked bread doughs, so this dough might be stiffer than you’re used to. If you don’t have a steamer (I don’t), you can build one! All you need is a pot with a lid and a small bowl or plate to raise the buns above the water level. Take a look at my video for this recipe to see.

Compared to baked buns, steamed buns are shinier and paler.

Conclusions

In both the filling and the dough, thousands of chemical reactions occur behind the scenes to create these pumpkin spice custard buns. In the filling, egg proteins align just right to thicken the custard along with cornstarch. In the dough, cornstarch adds tenderness by reducing gluten structure. The result is a warm, spiced twist on 奶黃包 egg custard buns!



References

Corriher, S. O. Bakewise; Scribner: New York, 2008.

Corriher, S. O. Cookwise, 1st ed.; William Morrow and Company, Inc.: New York, 1997.

Figoni, P. How Baking Works, 3rd ed.; John Wiley & Sons, Inc.: Hoboken, 2011.

Nelson, D. L.; Cox, M. M. Lehninger Principles of Biochemistry, 6th ed.; Freeman, W. H. & Company: New York, 2012.

Tako, M.; Tamaki, Y.; Teruya, T.; Takeda, Y. The Principles of Starch Gelatinization and Retrogradation. Food and Nutrition Sciences, 5, 280–291, 2014.

Leave a Reply

Your email address will not be published.

%d bloggers like this: