Step 1

Preheat oven to 180°C. Place an oven shelf in the lowest position and remove the other shelves.

Step 2

Place red onions in an ovenproof dish. Combine sugar, butter, red wine vinegar, balsamic vinegar and bay leaves in a heatproof jug. Season with salt and pepper. Pour over the red onions and toss to coat. Cover with foil. Roast in preheated oven for 30 minutes. Add spring onions and cook, covered, for a further 30 minutes. Remove foil and cook, for a further 30 minutes or until onions are tender. Cover with foil and set aside until required.

Step 3

Unwrap ham, rinse briefly under cold water and pat dry with paper towel.

Step 4

Use a small sharp knife to cut around ham shank in a zigzag pattern, about 10cm from end. Carefully run knife under rind around edge of ham. Gently lift rind in 1 piece, running your fingers between rind and fat where still joined. Lift rind off in 1 piece, wrap in a damp tea towel and place in the fridge. Use for storing leftover ham (see note).

Step 5

Trim excess fat from ham, leaving a 1cm-thick covering all over. Use a knife to score fat in a diamond pattern, 5mm deep. Pour a small amount of water in a roasting pan. Place ham on a wire rack in the pan. Wrap overhanging shank in foil to prevent juices dripping into oven.

Step 6

To make the glaze, heat the marmalade in a saucepan over medium heat for 5-7 minutes or until melted and just beginning to bubble. Add port and mix until combined. Pour half the glaze over ham, using a spatula to spread evenly over surface. Stud each diamond with a clove. Add peppercorns to remaining glaze. Bake ham in preheated oven for 1 hour.

Step 7

Remove from oven. Increase heat to 220°C. Pour remaining glaze over ham and spread evenly. Turn pan 180°, bake for a further 20 minutes or until well browned. Remove from oven. Rest for 15 minutes before carving.

Step 8

Meanwhile, return roast onions to oven and cook, covered, for 15 minutes or until heated through.

Step 9

Carve the ham (see note) and serve with the roast onions.