Put yeast in water milk mixture, wait for 10 min until it rises. Then put it in flour, knead. Then put the dough in bowl and cover with foil for one and a half hour to two.
Mix all ingredients in ground pork and mix until combined. Then add a small cup of water by 3 times, mix until the filling is smooth and loose.
Knead the dough to press out air bubbles. cut them into at least 24 little buns. knead the bun to round and press air out again. Roll into round sheet with middle part thick and the edge thin. Make Baozi.
Put the Baozi in air for second rising and not cover it for a little hard shell. Put in steam pan with cold water and heat until boil. 15 min the Baozi will be done and let them sit for 3 min until open the lid.