Preheat the oven to 230C/210C fan/Gas 8.
For the roast pork belly, put the pork belly in a roasting tray, skin-side up. Thoroughly pat it dry with kitchen paper, then rub sea salt all over the skin. Set aside for 20 minutes.
Roast the pork belly for 30 minutes, then reduce the oven temperature to 160C/140C fan/Gas 3 and continue to cook for a further 1½ hours. When cooked, set the pork aside to rest in a warm place.
Meanwhile, for the rib gravy, heat the oil in large saucepan over a medium heat. Add the pork ribs and fry for 3-4 minutes on each side, turning them regularly until they have caramelised all over. Remove from the pan and set aside.
Add the onions and carrots to the pan, then pour over the stock. Bring to the boil, scraping any burned bits up from the bottom of the pan using a wooden spoon.
Return the browned pork ribs to the pan, then add the peppercorns, bay leaves and thyme. Reduce the heat until the mixture is simmering, then continue to simmer gently for 1½ hours.
Meanwhile, for the apple bread sauce, heat the milk in a large saucepan. Stud the onion with 3 of the cloves and add to the hot milk. Stud one of the apples with the remaining 2 cloves and add to the pan along with the cinnamon stick. As the milk starts to bubble, turn off the heat, cover the pan with a lid and leave to infuse for at least 30 minutes. Once infused, discard the apple, onion, cloves and cinnamon stick.
Add the breadcrumbs and butter to the infused milk, stir well and heat gently. Just before serving, grate in the remaining apple and stir in the ground cinnamon.
When the cooking time for the pork ribs has elapsed, remove the ribs and slide the meat from the bone. Chop the meat and return it to the gravy mixture.
To serve, carve the pork belly and arrange the slices onto a serving platter. Serve the rib gravy in a large jug alongside and the apple bread sauce in a large serving bowl. Allow everyone to help themselves.