To make the bun dough, add yeast to water and let it activate for 10 minutes or until frothy. Add the remaining dry ingredients in the bowl of a stand-mixer with a dough hook.
Pour the yeast water into the bowl and start mixing on low speed until it forms a rough dough. Keep kneading the dough for another 5 minutes until the dough feels smooth and elastic.
Grease a bowl with oil and put dough inside, cover with cling film and let it rest for 1 hour until the dough has doubled in size.
Punch the air out of the dough, transfer it to a floured surface and spread it out into a 40cmx15cm rectangle, then roll it into a tight log. Cut the log into 12 equal size pieces, about 35-40 grams each.
Flatten each dough then roll them up into balls. Place them on a baking tray lined with baking paper, cover with tea towel and let it rest for 30 minutes. It will double in size again.
In the mean time, cut out twelve 8cmx8cm squares of baking paper. Take one dough and using a rolling pin, roll the dough into a 8cmx15cm oval shape, dip a chopstick in vegetable oil and place it in the center of the oval, fold it in half then pull the chopstick out.
Place the bun on a square of baking paper and put it back on the baking tray, repeat with the rest of the dough. Once completed, cover with tea towel and let it proof for another 30 minutes.
Set up a steamer over simmering water, in batches and steam the buns for 10 minutes.