Preheat the oven to 220c, 200 fan, gas 7. Line a roasting tin with a sheet of foil large enough to cover the pork later and put it to one side for now. Remove the string from the pork, unroll it, pat dry. Take the skin off the meat carefully
Mix together the salt, black pepper, onion powder, sage and sugar and rub the mixture all over the pork. Roll up again and roast in a tin in the oven for 15 minutes. Leave the pork skin to one side.
Turn the oven down to 150/130 fan Gas mark 2. Remove the pork, add the onions to the base of the roasting tin, put the pork on top and fold the foil over the top. Return to the oven and cook for at least 5 hours until tender and ready to pull apart.
Remove from oven, still under the foil and rest for 30 minutes in a warm place.
For the caramelised apples, core and cut the apples in half. Melt the butter in a large frying pan and stir in the sugar. Add the apples upside down and cook over a medium heat shaking the pan occasionally until the apples are lightly caramelised. Carefully turn the apples over and cook for a further 4-5mins until soft.
With two forks shred the pork into chunky pieces in the cooking juices and serve with the apples, onions and crackling.
Leave the pork skin at room temperature to dry. Rub in lots of salt and cook In a really hot oven for 30 minutes until crisp. Chop into small pieces.