Step 1

Put the pork belly in the fridge overnight, leaving the skin exposed to dry. The next day, use a sharp knife to score the skin in 1cm intervals, being careful not to go through to the meat. Mix together 1 tbsp of the sea salt, the thyme leaves and black pepper, and rub thoroughly onto the meat but not the skin. Chill, uncovered, for 1 hour, then remove from the fridge for another hour to come back to room temperature.

Step 2

Heat the oven to 230C/fan 210C/gas Rub a drizzle of oil over the skin and season with the remaining sea salt, making sure to get it between the scored cuts.

Step 3

Put the onions and celery sticks into a large, deep baking tray, then sit the pork on top, skin-side up, and roast for 45 minutes, until starting to crisp.

Step 4

Turn down the heat to 160C/fan 140C/gas 3, pour the chicken stock and cider around the meat (being careful not to touch the skin), and roast for a further 3 hours. The meat should be very tender and the crackling crisp – if it’s not quite done, turn up the oven to 200C/fan 180C/gas 6 and roast for a further 15-20 minutes or until really crisp.

Step 5

Move the pork onto a serving or carving plate with the onions, and loosely cover with foil. Pour the juices into a jug and allow them to settle. Skim off the fat, then pour the cooking juices into a pan and top up with just-boiled water if it tastes a little strong. Whisk in the wholegrain mustard.

Step 6

Carve the meat and serve with the onions, celery and gravy.