Preheat the oven to 170c (fan oven 150c), gas mark 3.
Put the belly of pork in a large roasting tin and add the cider, stock and rosemary. Bring to the boil on the hob, then cover tightly with foil and poach in the preheated oven for 3 hours. Leave to cool.
Meanwhile, in a pestle and mortar or a strong bowl with the end of a rolling pin, pound the garlic, olive oil, 2 teaspoons of the salt and the fennel seeds to a rough paste. Add 2 tablespoons of the marmalade and pound for a further few seconds.
Raise the oven temperature to 220C (fan oven 200C), gas mark 7.
Drain the pork, reserving the cooking liquid. With a sharp knife, cut away the rind from the pork fat and set it aside on a large piece of foil. Score the fat with a sharp knife.
Rinse out the roasting tin, return the meat to the tin and spread the fat with the marmalade mixture. Rub the pork rind with the remaining salt.
Put the pork in the oven, with the pork rind on a shelf above, and roast for 10 minutes. Reduce the temperature to 200C (fan oven 180C), gas mark 6, and continue to roast for a further 20-25 minutes until the pork is golden brown and the crackling crisp.
Meanwhile, put the poaching liquid in a large saucepan with the remaining marmalade and bring to the boil. Bubble for a good 10-15 minutes until reduced by about two-thirds.
Mash the flour into the butter and whisk into the liquid. Return to the boil, whisking all the time, and cook until lightly thickened. Adjust the seasoning to taste. Serve the pork carved into thick slices with shards of crispy crackling and the gravy.
To prepare ahead of time, poach the pork for 3 hours the day before it is needed. Drain, remove the rind and make the gravy. Keep everything covered in the fridge. When ready to use, allow the pork and rind 15 minutes at room temperature before roasting. Bring the gravy to the boil and simmer for 10 minutes until piping hot.
