Cut the pork belly into large slabs. Place in a pot with enough cold water, bring to a boil and continue cooking for 1 to 2 minutes. Transfer out, drain and clean.
Heat around 1 tablespoons of oil in a wok and then fry the pork belly until browned. Transfer to a simmering pot, add all the other ingredients and enough water except fried shallots, bring to a boil and continue cooking for around 1hour. Add fried shallots if you plan to use and continue simmering for 30 minutes to 50 minutes until the pork belly becomes really soft.
Steamed buns
In a stand mixer, mix all the ingredients for 9-12 minutes with hook and low speed until get a elastic, smooth and soft dough. Shape it to a large ball and cover with wet cloth. Set aside for proofing (around 1 hour).
When the dough is about 1.5 times in size, transfer out and re-knead until smooth in surface again (key step to smooth surface). Then divide into 8 portions. Knead each of the portions for 1 or 2 minutes until they are smooth. And then roll each of the small balls to an oval like shape.
Slightly dust the oval (or brush a layer of oil on surface) and fold the dough over by the middle.
Place them in steamer, turn up the fire and heat for 2-3 minutes, turn off the fire and wait for 15 minutes. Re-start the fire and steam the buns for 10 minutes after the water boils.
Fillings and sauce
Mix all the ingredients for optional Chili sauce.
Heat around 3 tablespoons of oil in wok and then fry minced pickled mustard green for 2-3 minutes until aroma.
Smash toasted peanuts and mix with 1 tablespoon of sugar powder.