Chinese Hamburger-Pork Belly Buns

Name: Chinese Hamburger-Pork Belly Buns
Prep time: 1 h
Cook time: 1 h
Total time: 2 h
Cuisine: Chinese
Ingredients: 200 g plain flour; pinch of salt; 1 tbsp. vegetable cooking oil; 100 ml water ( , note 1); 3/4 tsp. instant yeast; 800 g pork belly (, note 1); 1/2 cup crystal sugar; 2 large onion ( ,cut into sections ); 2 tbsp. light soy sauce; 1.5 tbsp. dark soy sauce; 1 inch root ginger ( , divided); Water or stock as needed; 1 tbsp. Shaoxing cooking wine; 1 tbsp. salt; 4 cloves garlic; 1 tsp. Sichuan peppercorn; 2 star anises; 1 small cinnamon bark; 4 ~6 cloves; 2 bay leaves; 1 tsp. fennel seeds; 1 dried chili pepper; 1 piece of dried tangerine peel; 1 tsp. whole white pepper; 1 chunk galangal (,optional ); 1 Fructus Amomi (, optional (砂仁)); 2 pieces of dried ginger (, optional); 1 piece of sand ginger ( , optional); 1 nutmeg (, optional (豆蔻)); 1 Tsaoko Amomum ( ,optional (草果))