• See Notes for achieving extra-crispy crackling and scoring. If you’re unable to, or forget to leave the pork uncovered overnight, pat the skin dry with kitchen roll, to get it as dry as possible, and salt it just before roasting, leaving the string on.
• Heat the oven to 220C/200C fan/gas 7. Just before roasting, rub the oil into the skin and into each cut. Sprinkle the salt over the skin in an even layer, rubbing this into the cuts too.
• Place the onion slices into a large roasting tin, in a single layer and sit the pork on top. Roast for 30 minutes, until the skin is blistering and bubbling.
• Pour enough boiling water around the joint, onto the onions, ensuring it doesn’t touch the skin. You want enough water for the onions to be covered and the joint to just be sitting in it. This helps to create a balance of crispy skin and tender meat. Reduce the temperature to 190C/170C fan/gas 5 and roast for another 1 hour 27 minutes.

Make the optional cider and onion gravy:

• Heat the oil in a medium saucepan over a medium heat. Add the onions and sauté for 4 to 5 minutes, until translucent and starting to go golden. Season with the salt and freshly ground black pepper, then sprinkle over the flour, stir well and cook for 1 minute. Add the brown sugar, dried sage or thyme, cider and stock. Stir to combine, bring to a fast simmer and cook uncovered for 25 minutes. Check the seasoning and add more if needed. Remove from the heat and set aside. The gravy can be reheated gently on the hob and transferred to a jug just before serving.

Rest, carve and serve:

• Check the pork is cooked using a meat thermometer – the internal temperature should be 63C. If required, return the pork to the oven to cook for a further 10 to 15 minutes, depending on the temperature reached when checked the first time.
• Once cooked, remove from the oven and place the pork on a board that will catch the resting juices. Rest for at least 15 minutes under loosely tented tin foil – this will keep the pork juicy while the crackling remains crisp. The liquid, fat and onions from the roasting tin can be discarded.
• Gently reheat the gravy and add any resting juices from the pork to add more flavour.
• Remove and discard the string from the pork, then remove the crackling in large pieces, and break it into smaller chunks. Carve the pork and serve it along with the crackling, gravy and your favourite sides.