Combine the All-Purpose Flour (525 gram), Salt (1/2 teaspoon) and Caster Sugar (1 1/2 tablespoon) in the bowl of a stand mixer with the dough hook attached.
Dissolve the Instant Dry Yeast (1 teaspoon), Caster Sugar (1 pinch) and Water (1 tablespoon) in a bowl.
Add the yeast mixture to the flour mixture, along with the Milk (50 milliliter), Sunflower Oil (1 tablespoon), Rice Vinegar (1 tablespoon) and Water (200 milliliter).
Knead for around 10 minutes, until the dough is smooth.
Place the dough in an oiled glass bowl, cover with a clean damp tea towel and place in a warm spot to prove for around 2 hours.
The dough should have doubled in size.
Place the dough back in the bowl of a stand mixer and add the Baking Powder (1 teaspoon) and knead into the dough for 5 minutes.
Roll out the dough into a long sausage, around 3cm thick.
Cut into pieces about 3cm wide. You should get around 16 to 18 pieces.
Roll each piece of dough into smooth balls and leave to rest for 2-3 minutes.
Use a rolling pin to roll out each ball, into an oval shape about 3-4mm thick.
Brush the surface of the dough ovals with a little bit Sunflower Oil (to taste).
Rub a chopstick with more sunflower oil and place in the centre of the dough.
Fold the dough over the chopstick.
Then slowly pull the chopstick out and place each bun on a lined baking tray covered with a clean tea towel. Allow to prove in a warm place for 1 hour and 30 minutes, or until they've doubled in size.
Heat a large steamer over a medium-high heat. Steam the buns for 8 mins until puffed up. Depending on the size of your steamer, you might have to do this in batches.