Place the flour, baking powder, instant yeast, and sugar in the mixing bowl of a stand mixer fitted with a whisk attachment. Whisk the dry ingredients together on low speed until thoroughly combined.
Swap the whisk attachment for a dough hook and slowly stream in the water and oil with the mixer set to a low speed.
Once all the liquid has been added, leave the mixer to knead the dough for 7-8 minutes or until the dough is smooth and slightly tacky to the touch.
Grease a large bowl with a little additional vegetable oil. Transfer the dough to the bowl and cover with a tea towel. Place the dough in a warm, dry place to rise. Let rise for 90 minutes or until doubled in size.
Once risen, punch the dough down and transfer to a well-floured surface. Knead the dough by hand for about 5 minutes to work out any residual air bubbles.
Using a floured rolling pin, roll out the dough to a 1/4" thickness. Using a 3" biscuit cutter, cut out a series of rounds. Brush a little vegetable oil on the surface of each round and fold them in half with the oiled surface inside.
Place each bao on 4x4" squares of parchment paper and transfer them to a large baking sheet. Cover with a tea towel and leave the bao to rise for 30 minutes.
Pour 2-inches of water into the base of a wok. Place the wok over high heat and bring to a boil. Fill a bamboo steamer with the boa and place the steamer in the wok. Leave the bao to steam for 7-10 minutes or until fluffy. Keep the finished bao warm until ready to serve.