1.Calculate the cooking time by allowing 20 minutes per kilogram. Preheat the oven to 160°C.
2.Slip your clean fingers under the ham’s skin to separate it from the fat layer. Slowly run your hand under the skin, peeling it away to expose a smooth layer of fat. Discard the skin.
3.Use a sharp knife to score a diamond pattern into the fat. Press a clove into the centre of each diamond then place the ham in a large roasting pan and bake for the calculated length of time.
4.Combine sugar, orange juice, brandy, marmalade and mustard in a small pot and heat gently until simmering. Simmer for 2 minutes then set aside. (The glaze can be made a day ahead if you prefer).
5.With 1 hour of cooking time remaining, remove pan from oven, tuck onion wedges around ham and liberally brush ham with glaze then return to oven. Repeat glazing at regular intervals, using remaining glaze and also spooning up the rich pan drippings to drizzle over both ham and onions.
6.Slice the ham and serve, warm or cold, with the sweet, sticky, roasted onion wedges.