To make the sauce

In a small bowl, combine the sauce ingredients and set aside.

To make the filling

Heat a wok over high heat for 40 seconds, add the peanut oil and coat the wok with it using a spatula.

When a wisp of white smoke appears, add the onion. Lower the heat to medium and cook for 5 minutes until the onion turns light brown.

Raise the heat, add the pork and cook, stirring for 2 minutes. Add the wine and mix well. Stir the sauce the pour into the wok, stir and mix, cooking for 1 to 1½ minutes until the sauce thickens and turns brown. Add the sesame oil and mix well.

Turn off the heat and transfer the filling mixture to a shallow dish. Cool to room temperature then refrigerate uncovered for 4 hours or covered overnight.

To make the dough**

Mix the flour, baking powder, and sugar together on a work surface. Make a well in the center, add the milk gradually, and with your fingers combine with the flour mixture.

When the milk is absorbed, add the water and work the dough with your fingers.

Add the lard or peanut oil and continue to work the dough with your fingers.

Using a dough scraper, gather the dough in one hand and knead for 12-15 minutes. If the dough is dry, add 1 teaspoon water at a time and continue to knead until the dough is elastic. If the dough is wet, sprinkle a bit of flour on the work surface and on your hands and continue working it. When the dough is elastic, cover with a damp cloth and allow to rest for 1 hour.

To make the bao

Roll the dough into a cylinder 16 inches long. Cut into 1-inch pieces. Roll each piece into a ball.

Work with 1 piece at a time, cover those not being used with a damp cloth. Press a ball of dough down lightly, then, with your fingers, press into a well-like shape. Place 1½ tablespoons filling into the well, close, and pleat the dough with your fingers until the filling is completely enclosed. Repeat for all 16 pieces of dough.

Place the buns on 2½-inch squares of wax paper and place in a bamboo steamer, allowing room for the buns to expand during cooking.

Heat water in a wok to steam the bao adding a tablespoon of white vinegar to the water (to make the buns a bright white).

Place the bamboo steamer in the wok and steam the bao for 15-20 minutes. If using two steamer trays, switch the trays halfway through cooking. Turn off the heat, remove the buns, and serve.