Add the milk to a large bowl, reserving 20 ml. to add if needed.
Sprinkle the yeast and sugar on the surface of milk. Whisk to dissolve.
Whisk in the salt and butter.
Stir in the flour and baking powder and work into a shaggy dough. Add the remaining milk if the dough seems to dry. Form the dough into a ball and place in a bowl and cover with plastic wrap to rest for 15 minutes.
Weigh out the red bean paste in to 10, 15 g. balls. Gently roll the balls in the palms of your hands to smooth out the surface.
Cut a 110 g. portion of dough, add 4 drops of orange paste food coloring. Knead until the food coloring is evenly distributed, cover with plastic wrap to rest for 20 minutes or until doubled in size.
Knead the remaining dough for 3-5 minutes or until the surface of the dough is smooth. Place into a bowl, cover with plastic wrap to rest for 20 minutes.
Cut and weigh out the orange dough into 10, 11 g. balls.
Cut and weigh out the white dough into 10, 30 g. balls.
Take a ball of white dough and using a rolling pin, roll it into a 4 inch circle. Then use the pin to thin the edge of the dough circle, rolling and turning the dough around the entire perimeter.
Place a ball of bean paste in the middle and using your thumb and index finger pleat the dough to encase the bean paste. Turn the dumpling over on to the work surface and use your hands to cup the dumpling and round it out.
Take a of orange dough a roll out a 5 inch circle. Place the red bean paste filled dumpling and place it upside down on the orange dough circle. Pull up the edges of the orange dough to encase the dumpling, pinching to seal. Place on a square of parchment.
Place a toothpick in the middle of each dumpling. Cover with plastic wrap and allow to proof 15-20 minutes or until a scrap of dough floats in a cup of water.
Place the buns in a steamer and steam on medium heat for 8 minutes.
After 8 minutes turn off the heat and place a chopstick under the lid of the steamer to allow the steam to escape gently and to prevent the bao from collapsing.