Time: about 3 hours
The Chinese make almost all of the world's favourite things today, including phony stuff. So I reckon it is time that I made a knockoff of a Chinese thing, a dumpling called liu sha bao, which is a mildy sweet, steamed runny-custard-filled bun. If the custard is a paste, then it is called lai wong bao.
This recipe is prototype 2.0, so it may change in the future.
In saucepan, whisk all custard ingredients together. Cook on medium heat, stirring always until mixture boils and thickens.
Activate yeast in the water with a pinch of sugar for about 15 minutes.
Mix all dough ingredients together, and the yeasty water—add a bit more water if the dough doesn't come together.
Kneed it til all lumpiness is gone, and it feels springy, then let it raise in a warm place in a lightly greased, covered pot for about 1 hour.
After that, get the dough and kneed it again for a minute (I think this is a good idea), then make a roll of it about as long as your forearm.
Slice the dough roll into 10 even pieces. Set steamer to boil.
Flatten dough slices by hand, dollop enough custard filler into their middles so that it won't spurt out as you pinch the dough sides together to wrap fillings fully.
Place each raw bun that you have just made on baking paper (brown paper works well) with seam sides down. Put the steamer off the boil so there is only steam in it.
Put the raw buns in steamer, and leave them to sit in the unboiling steam for a few minutes—my reasoning for doing this is so the buns will form a nice glaze on themselves.
Put the steamer with the buns back onto boil for about 8 minutes, at least. The buns double their sizes.
Serve at once, but they can be put aside and eaten later by heating them up—maybe with a coating of water if they've dried somewhat.