Tear out the stalks from the bay leaves, then bash the leaves in a pestle and mortar with a good pinch of sea salt to make a paste. Add the paprika and muddle in 1 tablespoon of olive oil.
Score the pork all over in a criss-cross fashion with a clean Stanley knife at 1cm intervals, just going through the fat, not the meat. Rub with the bay oil, getting into all the scores.
Peel and roughly chop the onions and sweet potato, peel and finely chop the garlic, halve the chillies, then place it all in a snug-fitting roasting tray or dish and sit the pork on top. Roast for 45 minutes.
Take the tray out of the oven and remove the pork to a plate momentarily.
Stir the vinegar and passata into the tray, half fill the empty passata jar with water, swirl it around and pour into the tray, then sit the pork back on top.
Reduce the oven temperature to 170°C/325°F/gas 3 and roast for a further 1½ hours.
Twenty minutes before the end, remove the pork from the oven and skim the fat from the surface into a small bowl.
Strip in the rosemary leaves (discarding the stalks), toss to coat, then sprinkle over the pork belly and place back in the oven for the remaining time, or until the pork is golden and tender and the sauce is reduced (loosen with a splash of extra water at the end, if needed).
The crackling should have puffed up nicely, but, if it hasn’t (pork skin can sometimes be erratic), just pop it under a hot grill and watch it like a hawk until it’s perfect. Serve in the middle of the table with your chosen sides (see below), and tuck in.