In a bowl, whisk together the two flours, sugar, salt, dry yeast, and baking powder.
150 g bread flour (10–12% protein), 150 g pastry flour (5–10% protein), 30 g sugar, 3 g salt, 6 g dry yeast, 3 g baking powder
Add the sake and about two-thirds of the warm water; stir, then add just enough of the remaining water to form a shaggy dough.
90 g warm water, 65 g sake
Knead on the counter for 10 minutes, work in the vegetable oil, then knead for another 5 minutes until the dough is smooth.
20 g vegetable oil
Shape the dough into a ball, cover, and let rise for 15 minutes at 30 °C.
Make the filling
Rehydrate the shiitake mushrooms, chop the onion and bamboo shoots, and grate the ginger.
150 g onion, 150 g bamboo shoots, 15 g dried shiitake mushrooms, 5 g ginger
In a bowl, combine the ground pork, prepared vegetables, soy sauce, oyster sauce, cooking sake, Wei-pa, sugar, sesame oil, salt, and pepper. Mix until sticky, then divide into 10 portions.
350 g ground pork, 2.5 tablespoons light soy sauce, 1.5 tablespoons oyster sauce, 2.5 tablespoons cooking sake, 1.5 teaspoons Wei-pa, 1.5 tablespoons sugar, 1.5 tablespoons sesame oil, salt and pepper
Shaping and steaming
Punch down the dough, divide into 10 pieces, shape each into a ball, cover, and rest for 10 minutes.
Flatten each piece into a round, keeping it thicker in the center; add a portion of filling, pleat to seal, then set each bao on a square of parchment paper.
Let the bao rise for 10 to 15 minutes at 35 °C.
Steam the bao over rapidly boiling water for 15 minutes, remove from the steamer, and serve hot.
Notes
Blanching bamboo shoots for 10 seconds removes their astringency and intensifies their aroma.
Keeping the dough slightly thicker in the center prevents tearing when the filling releases juices during steaming.