Heat your oven to 160°C/Fan 140°C/Gas 2. Remove the gammon from its packaging, leaving it in the netting. Give it a good rinse. Place in a large casserole dish or ovenproof pan and cover with water. Cover with a lid and bring to the boil, then simmer for 10 mins.
While the gammon cooks, trim the leeks and cut them into thirds. Peel, core and thickly slice the apples. Peel and thickly slice the onion. Roughly chop the sage, including the stalks.
Warm a large frying pan over a medium heat. Add 1 tbsp olive oil and the onion. Fry for 2 mins, then add the leeks. Season. Fry for 5 mins. Tip into a bowl. Add another 1 tbsp oil to the pan with the apples and sage. Fry for 5 mins till they begin to caramelise.
Drain and rinse the gammon, discarding the water. Rinse the pan and put the gammon back in. Tip in the leeks, onion and sagey apples. Pour over 1 ltr boiling water or homemade chicken stock. Add plenty of black pepper. Cover and slide into the oven.
Bake for 1 hr. Remove from the oven and turn the gammon in the water. Cover, put back in the oven and cook for 1 hr 30 mins. When cooked, remove the netting. Thickly slice the gammon and serve with the leek and apple sauce.
Shred any leftover gammon and stir into the leek and apple sauce with a can of butter beans. Top with chopped parsley. Or, shred any leftover gammon and stuff into a Pan Bagnat for a perfect (indoor) floor picnic! Find it at www.abelandcole.co.uk/recipes