Mix the dried yeast and lukewarm water. Allow it to sit for several minutes to activate.
Meanwhile, combine the baking powder, flour and sugar in a separate mixing bowl. After the yeast mixture has begun to bubble, gently pour it into the dry ingredients. Mix well then add the salt. (Be careful here as we don't want the salt to kill the yeast.
Addd the oil and knead for 3-5 minutes on a lightly floured surface for 3-5 minutes till the dough is smooth.
1st proof: Place the dough in a clean, oiled large bowl, and cover it with a damp kitchen towel/ plastic wrap. Rest the dough till it is doubled in size. It took me 1 hour at around 25C so it will take longer if you're living somewhere colder/ faster if you live somewhere hotter. (If you're adding a filling, you can use the time to prep the fillings.)
After the dough has doubled, punch it down to release the air then knead briefly to form a smooth texture. Divide the dough into 11 portions (about 35-40g), then shape the individual buns into a ball.
Cover and rest for 5-10 minutes to relax the gluten, then wrap your filling of choice.
If not using a filling, place each bun, seam down, on a small piece of parchment paper then place in the bamboo steamer, and cover. (For gua bao, you will need a rolling pin to roll the dough balls into oval shapes, fold, then steam.) 2nd proof: allow to rest for 20 minutes/
Steam the bao buns for about 7-8 minutes till soft and cooked through. Leave for 5 minutes before uncovering.