Prepare a pot of boiling water and an ice bath. Once the pot of water is boiling, blanch the bok choy for a quick 10 seconds in two separate batches. With each batch, the water should be at a rolling boil before you add the bok choy. With a large slotted spoon, scoop out the blanched bok choy and immediately transfer to the ice bath to stop the cooking process.
Strain the bok choy once it’s cooled completely in the ice bath. Do your best to squeeze out as much water as you can. This step is very important for preventing soggy buns!
Next, finely chop the bok choy; a food processor is a great time-saver. Transfer to a mixing bowl. Chop the mushrooms finely. Cook them in a wok over medium heat with 2 tablespoons of oil for about 3 to 4 minutes, until they become fragrant. Cool completely.
Next, finely chop the dried bean curd and set aside.
To finish the filling, first pour off any visible liquid in the bowl of chopped bok choy before adding in the cooked mushrooms and dried bean curd. Next, add 1 tablespoon of oil, the light soy sauce, sugar, sesame oil, and white pepper. Mix well. Salt to taste, and put the filling in the refrigerator to marinate. Chilling also helps to keep the bok choy green.
Making the dough
In a bowl, whisk together the water, yeast, and sugar until the yeast dissolves. Let the mixture sit until the yeast “blooms” and foams (about 15 minutes). Stir in 1 tablespoon of oil, and set aside.
In the meantime, whisk together the flour, cornstarch, salt, and baking soda in a medium bowl. Stir in the yeast mixture using a spatula. After the dry and wet ingredients are incorporated, knead the dough with your hands (or using a mixer) until the dough becomes smooth and soft. If the dough looks sticky, add a bit more flour 1 tablespoon at a time. If the dough feels dry, add a few drops of water at a time, and continue kneading until the dough is smooth and soft. The dough should be soft, but not sticky.
Brush the dough with 1 teaspoon of oil and cover with plastic wrap. Let the dough rest until it doubles in size (about 1 hour). Once the dough has risen, punch it down, and knead it for a few minutes to get rid of all air bubbles. Portion the dough into 14 equal dough balls. Cover with a clean kitchen towel to prevent them from drying out.
Assembling and cooking the buns
Cut 14 pieces of parchment paper into 3”x3” squares, and set aside. On a clean and lightly floured flat surface, take a dough ball, roll it out from edge to center, rotate, and repeat until it forms a 4-inch circle. The center should be slightly thicker than the edges. Your buns need solid footing, after all.
Add about 2½ tablespoons of filling to the center, then pleat and twist the bun repeatedly until the top is closed. Sit the bun on a piece of the prepared parchment paper and place it on the rack of your steaming vessel of choice, with at least 1 cm of clearance on all sides. Repeat until all the buns are assembled.
Check our Chinese cooking tools page for steamer setup options. You could use a steamer rack in a wok, a multi-level metal steamer or a bamboo steamer. Just make sure the steaming rack is at least 1½ inches above the water so the boiling water doesn’t touch the buns during the cooking process. Carefully put the buns inside the steamer, cover the lid, and let the buns rest for about 20 minutes (do not turn on the stove yet!).
When the buns are ready to be cooked, turn the heat on high to start the steaming process. Once the water starts to boil and steam is visible, turn the heat down to medium, and steam the buns for another 10 minutes. After 10 minutes, shut off the heat, and let the buns rest inside the steamer for 5 minutes. DO NOT REMOVE THE COVER. This is an important step, because if you remove the cover too early, the buns will collapse and lose their fluffiness! And if you are steaming buns in multiple batches, be sure to start each batch with cold water!
These buns can be enjoyed immediately. You can also store any leftovers in an airtight container in the refrigerator or freezer. Reheat in the microwave for about 1 minute or re-steam for about 6-8 minutes.