Xian rou bao zi (steamed pork buns)

Dough

• 250 g water
• 1 ½ tsp dried instant yeast
• 1 tsp baking powder
• 230 g baker's flour
• 200 g plain flour
• 50 g white sugar
• 1 tsp salt

Filling

• 5 spring onions/shallots, trimmed and cut into pieces
• 500 g pork mince
• ½ tsp ground white pepper
• 1 tsp white sugar
• ¼ tsp Chinese five spice powder (see Tips)
• 1 tbsp oyster sauce
• 2 tbsp soy sauce
• 2 tbsp sesame oil
• 1 tbsp Shaoxing wine (Chinese cooking wine)

Assembly and steaming

• oil, for greasing
• plain flour, for dusting
• 700 g water