Place the gammon in a large pan, cover with water and add the onion, peppercorns and bay leaf. Bring to the boil, cover partially with a lid and simmer gently for 25 minutes per 450g/1lb.
Let the joint cool a little in the stock then remove. Using a small sharp knife cut just under a corner of the skin, and carefully pull away the skin from the fat.
Heat the oven to 220°C fan, 200°C, gas mark 7. Mix together the orange juice and marmalade and spread evenly over the fat, then score into a diamond pattern with a sharp knife. Put on a baking tray and bake in the oven for 20 minutes until the glaze is sticky and golden. Leave to cool before carving.
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