For the dough: 300 g (2 1/2 cups) all-purpose or bao flour
4 g (1 1/4 tsp) instant yeast
40 g (3 tbsp) sugar
1 1/2 tsp baking powder
160 ml (2/3 cup) warm water
15 g (1 tbsp) neutral oil or lard
For the filling: 250 g (1/2 lb) char siu (Chinese barbecue pork), diced 1 cm
1 tbsp neutral oil
1 shallot, minced
1 1/2 tbsp oyster sauce
1 tbsp hoisin sauce
1 tbsp sugar
1 tsp dark soy sauce
120 ml (1/2 cup) chicken stock or water
1 1/2 tbsp cornstarch mixed with 2 tbsp water
1 tsp sesame oil
How to make it
Make the dough (10 min, plus 1 hr rise): Mix flour, yeast and sugar, add the warm water and oil, and knead 10 minutes until very smooth. Cover and rise until doubled, about 1 hour. (Add the baking powder in step 4.)
Make the filling (10 min, plus cooling): Heat the oil and soften the shallot 1 minute. Add oyster sauce, hoisin, sugar, dark soy and stock and bring to a boil. Stir in the cornstarch slurry until thick and glossy, then the sesame oil and char siu. Cool completely, then chill; cold filling is far easier to wrap.
Cut 12 squares of parchment, 8 cm (3 in) each.
Add the baking powder (5 min): Punch the dough down, flatten it, sprinkle with the baking powder and knead 2 minutes to work it in evenly.
Shape (20 min): Cut 12 pieces. Roll each into a 10 cm (4 in) circle, thinner at the edge. Put a heaping tablespoon of filling in the center, gather the edges up in pleats and twist shut. Set each, pleated side up, on a parchment square. Rest 15 to 20 minutes, covered, until slightly puffy.
Steam (12 min): Steam over rapidly boiling water, 5 cm apart, for 12 minutes. Turn off the heat and wait 2 minutes before opening the lid so they don't wrinkle.
Serve: Warm. Reheat leftovers by steaming 5 minutes.
Tips
Very hot steam is what makes the tops burst open; keep the water at a hard boil.
Leave the twisted top a little loose if you want the classic split.