Grind together the soaked red chillies, peppercorns, star anise, cassia bark, cloves, cumin seeds, chopped ginger, chopped garlic, tamarind and vinegar to a smooth paste, adding a little water if required.
Heat oil in a large saucepan, add onions and sauté until well browned. Add 100 ml water and let the mixture simmer for 3-4 minutes, stir well. Add tomato paste, red chilli powder, jaggery, the spice paste and salt, mix well and cook for a couple of minutes. Add a litre of water, bring to a boil, remove from heat and set aside.
In a thick bottomed saucepan, heat oil and sear the pork belly, ensuring all sides are a nice golden brown. Pour in the sauce and braise over medium heat for 45 minutes. Remove the pork belly, place on a chopping board and cut into one-inch strips. Place back into the pot and cook on low heat for a further 30 min or until the pork is tender.