11. Prepare the Steamed Bun Dough: In a large bowl, combine warm water, active dry yeast, and 10g of the granulated sugar. Let sit for 5 minutes until foamy. Add all-purpose flour, baking powder, the remaining 10g of granulated sugar, and vegetable oil to the yeast mixture. Knead the dough for 8-10 minutes until smooth and elastic. Place the dough in a lightly oiled bowl, cover with a damp cloth, and let it proof in a warm place for 60-90 minutes, or until doubled in size.
22. Shape the Steamed Buns: Once proofed, gently punch down the dough and divide it into 12 equal portions. Roll each portion into an oval shape, approximately 10cm long. Brush one side of each oval with a thin layer of vegetable oil, then fold it in half to create the classic gua bao shape. Place each shaped bun on a small square of parchment paper. Arrange the shaped buns on a steamer rack, ensuring space between them. Cover and let them proof for another 20-30 minutes.
33. Steam the Buns: Bring water to a rolling boil in a steamer. Place the steamer racks with the proofed buns over the boiling water. Steam for 10-12 minutes. Turn off the heat and let the buns rest in the steamer for 2-3 minutes before opening the lid to prevent shrinkage. Remove the steamed buns and set aside.