To make the bao dough, add the flour, sugar, salt, baking powder, yeast, vegetable oil, warm water, and warm milk into a mixer. Mix with a dough hook for about 3 minutes until combined.
Transfer the dough to a lightly floured surface and knead for 3 to 4 minutes until smooth.
Roll the dough out to about 3 mm thickness. Using a round cutter or a pint glass (about 11 cm diameter), cut out circles to make approximately 8 bao buns.
Brush the surface of each circle with vegetable oil, then fold in half. Place on a lined tray or plate and cover with a tea towel. Leave to prove for 1 1/2 to 2 hours until doubled in size.
To prepare the pork belly, heat a wok or pan with a little oil. Add the ginger and pork belly and fry until the pork is lightly browned on both sides.
Add the cinnamon sticks and star anise and stir for about 1 minute to release their aroma.
Mix all the braising sauce ingredients together and pour into the pan. Cover and simmer over medium heat for 50 to 55 minutes until the liquid has reduced and formed a sticky sauce coating the pork belly.
Once the bao buns have risen, place them in a steamer on their greaseproof paper and steam for 8 minutes.
Remove from the steamer and allow them to rest for 5 minutes before serving.
Fill the steamed bao buns with the braised five spice pork belly and enjoy.