Banh bao (steamed pork buns)

Name: Banh bao (steamed pork buns)
Prep time: 40 min
Cook time: 2 h 45 min
Total time: 2 h 45 min
Yield: 12 portions
Ingredients: 200 g full cream milk; 2 tsp dried instant yeast; 20 g sugar; 350 g self-raising flour; 1 tsp baking powder; 30 g vegetable oil; 10 g dried shiitake mushrooms; boiling water; 2000 g water; chilled water; 12 quail eggs; 2 spring onions/shallots; 20 sprigs fresh chives; 2 Chinese sausages; 500 g pork mince; 2 tsp rice wine vinegar; 2 tbsp oyster sauce; ¼ tsp salt; ¼ tsp ground black pepper; 1000 g water