Filling:
1/2 Tbs. oil
1/2 onion, diced
1 tsp sugar
1 Tbs. oyster sauce
1 Tbs. soy sauce
1 tsp sesame oil
1/2 lb. char siu, diced

1/2 C water
1 Tbs. cornstarch

Heat oil in a pan and cook the onion until
translucent.  Add the other ingredients except the water and
cornstarch.  Cook for a couple of minutes.  Mix the water and
cornstarch and add it to the pan.  Cook until it has thickened.  Set it
to the side and let it cool.

Dough:
2 eggs
3/4 C milk
2 Tbs. butter
4 Tbs. sugar
2 tsp salt
4 C flour
3 tsp yeast
1/4 C warm water

I used my bread machine on the dough cycle to make the dough. 

I think the recipe should work in a stand mixer or even if it's done by hand if you proof the yeast in the water with a Tbs of sugar and warm the milk and melt the butter.

When the dough has risen divide it into 16 equal portions for large or 20 portions for medium bao.  Flatten the dough into a circle (flatten the edges a little more than the center or else your bao will be flat or thin on top), fill with some of the filling, gather edges to the top and crimp it closed.  Place it crimp side down on a baking sheet.

Allow them to rise for 10-15 minutes and brush with an optional egg wash (1 egg whisked).  Bake at 350F for 15-20 minutes or until nicely browned on top.