When the meat is ready, add the cornstarch to thicken the pork mixture. Allow the mixture to cool.
For the dough: Combine the flour, sugar, yeast and baking powder in a large bowl. Add 18 ounces (2 1/4 cups) cold water and the cream to the dry ingredients. Knead the mixture until it becomes a dough. Portion the dough into 2-ounce balls, then flatten and fill each ball with 1 ounce of the pork filling and a quarter of an egg. Then roll into a bun and proof the siopao for about 1 hour.
Steam the buns and serve.