Pound all of the ingredients for the spice rub together using a pestle and mortar. You’ll end up with a coarse mixture. Transfer to a small bowl. Heat oven to 220C/200C fan/gas 7.
To prepare the spices that will be simmered with the pork, pound the cinnamon, ginger, lime leaves and peppercorns using a pestle and mortar to a rough paste. Add the garlic. Roughly break up the star anise – it’s much too strong if you pound it – and add that too. Tip the spice mixture into a flameproof roasting tin that the pork will fit into. Lay the pork on top, skin-side down. Add enough boiling water to come just up to the level of the meat. Bring to a simmer on the hob and cook for 20 mins.
Take the pork out of the water and pat it dry. Discard the water and spices in the tin, wash and dry. Set a rack inside the roasting tin and lay the pork on top, skin-side up. Spread the spice rub over the pork, then drizzle on a little oil and rub all over the pork. Sprinkle over some sea salt, put in the oven and cook for 20 mins, then turn the heat down to 180C/160C fan/gas 4 and cook for a further 45 mins. Finish under the grill for 10 mins to crisp up the skin.
Make the sauce while the pork is cooking. Heat the oil in a frying pan and cook the shallots over a medium heat until golden. Add the chilli, garlic, and ginger and cook for 2 mins, then add the sugar. Cook until the sugar caramelises – be careful not to burn it – then quickly add 300ml water (it will sizzle and spit a bit). Stir in the lime leaves, fish sauce, lime juice and peanut butter. Bring to a simmer, stirring to break down the peanut butter. Taste. I usually add a little tamarind paste, but you might prefer to add more lime juice or fish sauce. Serve the pork belly with the sauce, rice and greens.