Thanks Kimmyh, all useful info. My DIL's father is a Chinese chef and she said he buys flour. From the Chinese shop specially for the buns. I bought some yesterday, some has everything added except the liquid, and the other is just the flour. Both say to add a little vinegar to the steaming water to keep the dough white, also to wipe any steam off the lid in the last 10 mins. Of steaming.
Tomorrow might be the day as I am cooking the filling today.