First, make the dough. Combine yeast and sugar in a bowl. Whisk to combine, then set aside for 5 minutes, or until frothy.
Place flour, baking powder and salt in the bowl of a stand mixer fitted with a bread hook. Stir to combine. Add yeast mixture, oil and milk and beat on low until combined. Increase speed to medium and beat for 5 minutes. Grease a large bowl with oil and transfer dough to bowl. Set aside for 45 minutes to proof.
While mixture proofs, prepare filling. Dice pork into 2cm cubes.
Combine honey, sherry, soy and oyster sauces, five-spice and sugar in a bowl. Set aside.
Heat olive oil in a large frying pan. Add pork and cook until browned, about 4 minutes. Add sauce and bring to the boil. Reduce heat and gently simmer mixture for 5 minutes. Remove from heat.
Divide dough into 15 equal-sized balls. Flatten in your palm and place a spoon of filling into the centre. Enclose dough around filling and roll in hands to create a ball. Repeat with remaining dough and filling.
Place a large saucepan on the stove and 1/3 fill with water. Bring to the boil over high heat. Line a large bamboo steamer with baking paper and place over saucepan. Arrange 4 buns into the steamer. Cover with steamer lid. Cook for 8 minutes, or until a skewer inserted into centre comes out clean. Keep warm. Repeat with remaining buns. Serve.