Fry the onions in the oil until soft in a large casserole. Add garlic then fry for a further minute or so before adding the rest of the ingredients. Bring to a gentle simmer and bake until the beans are soft and tender, roughly 3 hours.
Meanwhile whisk together salt and sugar. In a tray spread this mixture in the bottom and place the pork belly, skin side down, on top. Leave to sit in the fridge for around 3 hours.
Place the pork in the oven and bake for 2 hours, then turn the oven up to 220°C and blast for a further 30 minutes to crisp up the skin.
