Soak the gammon for several hours or overnight in cold water. Peel, core and quarter the apples and arrange over the base of a large saucepan. Add the onion stuck with the clove and the bay leaf. Set the piece of gammon on top of the apples and add the cider; it should be just sufficient to cover the apples: Cover the pan and bring up to the boil. Simmer gently allowing 30 minutes per
Lift the gammon from the pan and, using a small sharp knife, strip away the rind. Score the fat in a criss-cross pattern. Spread with the mustard, then coat with the demerara sugar and finally stick in a few cloves. Set in a roasting tin, place in the centre of a moderately hot oven (200°C., 400°F., Gas Mark 6) and bake for 15–20 minutes, until glazed and brown.
Meanwhile strain off the cooking liquor, reserving the apples. Remove the onion and bay leaf and return the apples to the saucepan. Stir to break them up to a purée and add the sugar and butter. Heat gently, allowing any excess moisture to boil away. Serve the apple sauce with the sliced gammon.