In a stand mixer bowl, add all of the starter, warm water, vinegar, sugar, all-purpose flour, milk powder, coconut oil and baking powder.
With the dough hook attachment, turn on low speed for 3 minutes, then turn higher speed for 7 minutes.
Remove dough onto the counter, knead to form smooth dough.
Divide into 8 portions and form into very small tight round balls. Cover with cling wrap to rest for 15 minutes.
Highly dust counter with flour. Flatten each dough ball into 6" disc with rolling pin. Repeat with the rest.
Re-roll dough, thinner on the edges into 6.5" diameter. Place a meat filling in the center. Gather edges, pleat and pinch 16-18 pleats to enclose the filling. Continue to pleat on the 2nd tier, to completely seal the hole.
Place bun on a 3.5" parchment square on a large baking sheet pan.
Place the pan in a warm location to proof for 40 minutes, until almost doubled in size.
Place buns into bamboo steamer (you may need more than 1 layer). Stack onto a large pot or wok with 2" of cold water underneath. Turn on highest heat.
Once steam is coming out of the lid, steam the buns for 20 minutes. After steaming for 5 minutes at high heat, turn heat down to medium high for 15 minutes, for a total of 20 minutes.
Turn off heat and let it sit for 5 minutes on the stove. Then remove bamboo steamer out of the stove to a cooling rack.
Slightly open the steamer lid a little bit to let steam dissipate, about 5 minutes, before removing the buns.