Transfer the starter mixture from the night before in to a larger bowl.
Add 2g baking ammonia dissolved in 2 tsp of water + 1 ml lye water. (Be careful, it will smell!)
Knead in the 60g granulated sugar, until it dissolves a little.
Add in the cake flour, wheat starch and baking powder.
Add in the milk, coconut oil, and vinegar.
Knead until the dough comes together.
Cover the bowl with a plate or plastic wrap and leave it to rest for about 30 minutes in a warm location.
When the dough shows some bubbles and has risen a little, lightly dust the work surface with some wheat starch and divide the dough into 10 equal portions. (About 45-50g each).
Roll the portioned dough into a flat disc and place a scoop of char siu BBQ pork filling (about 25-30g) in the centre.
Gather the dough up in 3 places, forming a triangular shape (like a samosa).
Gently press the centre down, and gather the sides up, forming a "bulb/tulip."
Pinch the 3 seams together on the sides.
Place the bun onto a piece of parchment paper or muffin liner.
Repeat with the remaining dough and filling.
Cover the buns with some plastic wrap and leave to rest in a warm location for about 20-30 minutes.