Combine warm water, sugar, and yeast in a measuring cup or bowl. Stir with a spoon to mix and allow yeast granules to dissolve, about 5 to 10 minutes.
Place bao flour/all-purpose flour in a large bowl. Add powdered/icing sugar and stir to combine. Make a well in the center of the bao flour.
Pour proofed yeast mixture into the well of the bao flour. Stir and mix with a spatula. Also, give it a quick knead to bring the dough together.
Add vegetable oil and continue mixing to form a dough ball. Cover bowl with plastic wrap and allow it to rest for 5 minutes.
After 5 minutes, continue to knead the dough until it is smooth, about 3 minutes.
Cover the bowl with plastic wrap and allow dough to rise in a warm place for about 1¼ hours or until double in size.
Filling
Heat vegetable oil in a medium size pan over medium heat. Saute garlic, onion, and carrots for 2 to 3 minutes.
Add char siu, honey, and hoisin sauce. Stir and add water. Cook for 3 minutes.
Pour in corn starch mixture and allow sauce to thicken. Turn off stove.
Stir in green onions. Transfer to a bowl and allow filling to cool completely.
Preparing Dough Wrappers
When dough has more or less doubled in size, remove the plastic and gently gather and flip the dough.
Sprinkle baking powder all over the dough. Knead until all baking powder is incorporated.
Remove dough from bowl and continue to knead on a lightly floured surface for 4 to 5 minutes.
Roll dough into a longish shape and divide it into two.
Roll a portion of the dough into a long cylinder and tear into 10 equal pieces. Place the pieces of dough into the bowl and cover the bowl with plastic to prevent them from drying. Do the same for the other portion of dough.
Wrapping Baos
Shape a piece of dough into a ball. Then, flatten it into a disk. Using a small rolling pin, roll out the edges to form a wrapper of about 4 inches in diameter with a slightly thicker center and tapered edges.
Place the dough wrapper on your palm and a rounded tablespoon of filling in the middle of wrapper. Gather and pleat the edges with your thumb and index finger.
Then twist and pinch to seal.
Place seam side up onto a piece of prepared parchment paper in a steaming rack. Repeat with remaining dough. Do not crowd the rack with too many baos as they will expand during steaming.
Steaming the Baos
Place steaming rack over a pot of cold water on the stove. If you are using a metal rack and lid, place a towel over the rack. Omit towel if you are using a bamboo rack. Cover with lid and turn on the stove over medium high heat.
When water comes to a rapid boil, allow the baos to steam for 12 minutes.
After 12 minutes, turn off the stove. Wait for 5 minutes before opening the lid and removing the steamed baos.
Steam in batches if necessary.
Notes
Leftover steamed baos may be placed in zip top plastic bag and kept in the freezer. Steam frozen buns for 8 to 10 minutes before serving.