Xian rou bao zi (steamed pork buns)

Name: Xian rou bao zi (steamed pork buns)
Prep time: 30 min
Cook time: 2 h 30 min
Total time: 2 h 30 min
Yield: 24 pieces
Ingredients: 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; 5 spring onions/shallots; 500 g pork mince; ½ tsp ground white pepper; 1 tsp white sugar; ¼ tsp Chinese five spice powder; 1 tbsp oyster sauce; 2 tbsp soy sauce; 2 tbsp sesame oil; 1 tbsp Shaoxing wine; oil; plain flour; 700 g water