Soak the beans overnight in fresh cold water.
Preheat the oven to 140°C.
Drain beans and place in a heavy casserole with fresh water covering them by 5cm.
Boil hard for 10 minutes then simmer covered for one hour until tender.
Cut pork belly into 5cm cubes and add to the beans.
Stir in the brown sugar, black treacle, and mustard.
Press cloves into one onion and add all onions to the pot with pepper.
Add hot water if needed to ensure beans are covered and bake covered for three hours.
Remove lid, move pork chunks to the top, and bake uncovered for one more hour.
Season with salt and pepper to taste before serving.