In a stand mixer bowl, combine the flour, sugar, instant yeast, and baking powder. Add the warm water and mix until a shaggy dough forms.
Knead on medium speed for 8 minutes, then finish with 2 minutes of hand kneading (alternatively knead by hand for 12 minutes). The dough should be very smooth.
Shape the dough into a ball then brush with a tiny bit of oil so that a skin doesn't form on the outside. Place it back in the stand mixer bowl and cover with plastic wrap. Let it rise for 1-2 hours until it is doubled in size.
Divide a sheet of parchment paper into twelve 4-inch squares.
Punch down the dough, then use a dough scraper to divide the dough into 12 equal portions.
For each dough portion, use a rolling pin to roll into a flat disc (this is to push out air bubbles). Then, form a smooth ball by pinching and tucking the ends underneath. Place onto the parchment paper.
Arrange the buns in a bamboo steamer with at least 2 inches of space between each one. Cover with plastic wrap and let them rise for 30 minutes to 1 ½ hours until 1.5x bigger.
Bring a pot of boil to a boil, then reduce the heat to medium-low (we want to cook the buns on a very gentle heat). Steam the buns for 12 minutes without opening the lid. Turn off the heat and let the residual heat steam them for another 5 minutes. Remove the buns and enjoy!