Place the gammon in a large casserole pot big enough to fit the lid on comfortably. Add the onion, orange juice and carcasses, ginger slices, ginger beer and spices. Top the liquid up with boiling water if necessary so the gammon is just covered with liquid. Bring to the boil, skimming off any impurities which rise to the top with a large spoon. Put a lid on, then turn the heat down to a gentle simmer and cook for 2 hours, turning the gammon halfway through. Alternatively cook on low in a slow cooker for the same amount of time.

Preheat the oven to 180°C fan/200°C. Once the gammon has had two hours, leave to cool slightly in the liquid and remove a couple of ladlefuls of the cooking liquid and add to a saucepan. Reduce over a high heat until only 3 tbsps liquid remains and add to a jug with the rest of the ingredients for the glaze. Mix well.

Place the gammon in a lined baking tray and cut away the skin, leaving behind a thin layer of fat. Pour over 200ml of the cooking liquid from the ham and then pour over half of the glaze. Roast for 15 minutes, basting the ham in the juices from the bottom of the tray, then pour over most of the rest of the glaze, leaving roughly 1 tbsp behind. Return to the oven for another 15 minutes.

Remove the ham, baste it again with the juices from the tray and pour over the remaining glaze. Cover with foil and leave to rest for 20 minutes before carving into slices. Reduce the liquid left in the roasting tray until thick and syrupy, adding any of the resting juices from the ham.

Serve with festive sides of your choice.