About an hour or so before cooking, take the pork out of the fridge and rub the skin well with salt. Put to one side – the salt will draw moisture out of the skin (creating better crackling), while the time elapsed before cooking allows the pork to warm to room temperature (which is better for an even roast). Season the meat and make small incisions in the flesh, then poke in a few slices of garlic and rosemary.
Heat the oven to 240C/fan 220C/gas 9. Stand the meat on a roasting tray with the skin facing up and roast for 20 minutes. Turn the heat down to 190C/fan 170C/gas 5 and cook for a further hour, or until the core temperature has reached 68C when checked with a meat thermometer. Rest in a warm spot for 15 minutes before serving; but don’t cover – you’ll spoil the crackling if you do.
While the pork cooks, tip the apples into a pan with the sugar and a splash of water, then stir on a medium heat for 10-15 minutes or until they have broken down to a near purée. Take off the heat, cool for 10 minutes then stir in the horseradish and lemon juice. Carve the pork and serve with the sauce and crackling.