Dissolve the yeast and a pinch of sugar in 1 bao bun recipe warm water, then add it to the flour with the milk, sunflower oil, rice vinegar and 200ml water. Mix into a dough, adding a little extra water if needed.
Tip the dough onto a lightly floured work surface and knead for 10-15 mins, or until smooth. Put in a lightly oiled bowl, cover with a damp cloth and leave to rise for 2 hrs, or until doubled in size. Tip the dough out onto a clean work surface and punch it down. Flatten the dough with your hands, then sprinkle over the baking powder and knead for 5 mins. In the palm of your hand, roll each piece of dough into a ball and leave to rest for 2-3 mins. Use a rolling pin to roll out each ball, one by one, into an oval shape about 3-4mm thick.
Rub the surface of the dough ovals with oil and brush a little oil over a chopstick. Place the oiled chopstick in the centre of each oval. Fold the dough over the chopstick, then slowly pull out the chopstick. Cut 18 squares of baking parchment and put a bun on each.
Transfer to a baking tray, cover with a clean tea towel and leave to prove in a warm place for 1 hr 30 mins, or until doubled in size. Heat a large steamer over a medium-high heat. RECIPE TIPSUSING A MIXER The dough can easily be made in a mixer with a dough hook up to the end of step 3. FREEZING THE BUNS The buns can be steamed, then frozen. Once defrosted, simply reheat in a steamer. This website is published by Immediate Media Company Limited under licence from BBC Studios Distribution. The sandwich was first created in the early 20th century after marshmallow creme, a sweet marshmallow-like spread, was invented in Massachusetts.