Once doubled, transfer the dough onto a lightly floured work surface. Divide dough into equal pieces and roll into a smooth ball. Let it rest for 15 minutes.
While the dough is resting, make the butter milk filling: first cream together the butter and powdered sugar. Then, mix in egg until the mixture is light and fluffy. Finally, add in salt, corn starch and milk powder. The mixture should be thick. Divide into 4 equal pieces and roll into balls.
Flatten the dough balls into a circle. Add the butter milk filling to the center and enclose it with dough, pinches the ends closed. Tightly roll into smooth balls and place it seam side down in the baking dish. Repeat with the rest. Let rise ~2-3 hours.
Preheat the oven to 350F. Make the egg wash and brush it on top on the risen dough. Alternatively, you can brush the top of the dough with warm milk, cream or coconut cream. Bake for 25 minutes or until the top turns golden brown.
Notes
Credits: Butter milk paste recipe adapted from thebakedbeaan