Start by making the bao buns, Place the flour, sugar, salt, and yeast in a bowl and mix together.
Add the milk, warm water, and butter to a jug and stir together until the butter melts.
Stir the liquid mixture into the flour mixture at first with a spoon, and then with your hands. Turn out onto a floured surface and knead for 10 minutes. Alternatively, you can do this in a mixer fitted with a dough hook.
Place the dough in an oiled bowl. Cover and leave to prove until doubled in size - about 90 minutes - 2 hours.
Meanwhile, start on the Korean Chicken. Place the chicken in a bowl. Add the buttermilk, salt, pepper and garlic salt. Mix together, cover and place in the fridge to marinade for at least 1 hour.
After the dough has proved, tip it out of the bowl onto a floured surface. Knead the dough again and split it into 20 balls. Place a piece of baking parchment on your work surface and roll each ball into an oval 6cm x 9cm.
Brush the ovals with the olive oil and fold each oval over, using a chopstick in the middle to fold over. Remove the chopstick and place each bun onto a small piece of baking parchment.
Place the buns on the trays still on the baking parchment. Cover each tray and leave to prove for a further hour, until puffed up.
Preheat the oven to a low heat. Heat a large pan of vegetable oil until hot. You’ll need at least 1 litre (4 cups) of oil.