I've been trying to make char sui bao for years and years. While I find the filling to be pretty easy to duplicate the bread part is not. Usually what happens is they don't rise in the steamer but become water laden and heavy.
I've tried just regular yeast bread dough recipes but they either over-rise and fall or just become heavy.
I have a recipe from a Chinese woman I used to work with which has both baking powder and yeast and an egg. It still comes out heavy and flat but it was closer. I suspect that egg is not a regular component of the restaurant bao-tze because they are very white and the yolk turns this dough a little yellow.
Yesterday I tried the recipe from Fuschia Dunlop's book Land of Plenty which has no salt but just yeast, sugar, flour and water. They were terrible. The dough rose beautifully before forming but didn't rise in the steamer. She does not advise you to let the dough rise after shaping but because I had too much dough for my steamer I formed and cooked half and let the second half rise before cooking. Both lots were not only heavy but tasted unpleasantly yeasty, almost alcoholic.
Just some notes:
I know it isn't the yeast as I have tried many times over the years with yeast that is very successful at breadmaking. I don't have trouble making bread!
I am in Canada and I know our flour is high in protein but the restaurants around here use the same flour yet they make good, soft, fluffy bao. I don't always like their filling so would like to make my own. The point is that recipes that have been tested with US flour may not work with my flour. My all-purpose flour has 4 g of protein per 30 g serving if that helps. Cake flour here is 2 g per 30 g serving.
The steamer I am using is a regulation full wok bamboo steamer inherited from my northern Chinese mother-in-law who unfortunately passed away without passing on her recipe for bao though my husband says she was never happy with hers either. I have tried letting the steamer fill with steam before putting the bao in thinking the problem was starting with a cold steamer. Doesn't seem to matter.
Sorry for the long post but thought it might help someone figure out what I am doing wrong.