Prepare the ingredients: Dice the pork belly into large rectangles about 1½ inches by 2 inches. Slice the ginger, with the skin on, into 7 slices (about ¼–⅓ inch thick) and cut the scallions into roughly 3–4 inch pieces.
Put the pork, 2 slices of ginger and 1 of the scallions into a pot and fill it with cold water. Bring it to a boil, let the pork cook for 2–3 minutes, then skim off any foam that floats to the surface. This will remove some of the unpleasant “sweaty” taste that is sometimes present in pork. Drain the pork, rinse it and pat it dry. Make sure it is completely dry or the meat won’t brown in the pan.
Fill a kettle with water and bring it to a boil.
Add a tablespoon of oil to a large wok or heavy pot, like a Dutch oven, and heat it over medium. Drop in the remaining ginger and scallions and fry them until fragrant (about 1 minute). Add the pork to the wok and fry it, turning the pieces occasionally, until they are browned on all sides. Add the bay leaves, star anise, Sichuan pepper and chillies to the wok and fry them for a minute, then remove everything with a slotted spoon, leaving the oil and fat from the meat in the pan.
Reduce the heat to low. There should still be fat in the pot from the cooked pork, but if not, add enough to cover the base of the pot (about 1 teaspoon). Add the sugar and cook it without stirring until it has dissolved into the oil and is thick like caramel; you can tilt the pot a bit to move the sugar around. (If you stir the sugar, it will start to crystallize and feel grainy and hard.) Watch the sugar carefully; you want it deeply brown and caramelised but you don’t want it to burn, which can happen quickly. This process can take anywhere from 2–5 minutes.
Once the sugar is thick and brown, turn up the heat to medium, add the pork and aromatics back into the pot and toss everything together so the pork is nicely coated in the caramel.
Pour in the Shaoxing wine and let it bubble for 10 seconds, then add the soy sauces. Toss the ingredients together, to mix everything, and then pour in enough boiling water to cover the meat. Bring the whole mixture to a boil, then reduce the heat until the sauce is just simmering, and cover the pot. Simmer everything together for 50 minutes.
Add the chestnuts to the pot, stir everything a bit, then cover the pot again and simmer for another 30 minutes.
Remove the lid from the pot but keep simmering everything for a final 10 minutes or until the meat is tender. At this point the sauce should reduce by about 10 percent. Taste for seasoning and add salt or a sprinkle of white sugar if you need it, then let the sauce continue reducing until it reaches your preferred thickness. The aim is not a thick glossy sauce; you want something closer to a broth. Serve with some steamed manto or hua juan buns to dip into the broth.
