Pre-heat the oven to 180°C.
For the gammon:
1. Place the gammon into a large, deep pan and cover with water. Bring to the boil, remove from the heat and drain. Return the gammon to the pan, cover the gammon with water and push two cloves into each onion half and then add the rest of the ingredients.
2. Place a lid and bring to the boil, then reduce the heat to a simmer. Cook gently for three hours, adding more hot water to the pan as necessary. Remove the gammon from the pan and place into a roasting tray. Remove the skin, leaving behind a thin layer of fat.
3. Score the gammon in a diamond pattern with the tip of a sharp knife. Stud the centre of each diamond with a clove.
For the glaze:
1. Mix together all of the glaze in a bowl until well combined. Spoon the glaze evenly over the gammon. Roast the gammon in the oven for 45 minutes, basting frequently with the glaze and pan juices, until the gammon is cooked through and golden-brown all over. Set aside to rest, then carve into thick slices to serve. Alternatively, the gammon can be eaten cold.
For the bubble and squeak:
1. Sprinkle a layer of salt in the bottom of a roasting dish ensuring it is fully covered. Place the potatoes, unpeeled, on top and cook for approximately one hour. During this time, place the sliced red onion and olive oil in a pan and cook slowly, without colouring until soft.
2. Shred the cabbage and place in boiling salted water for approximately one minute, until soft. Then place in a bowl of iced water. When the potatoes are cooked remove the flesh and add the butter, making a fairly dry mash. Remove the cabbage from the water and drain off any excess liquid using a dry towel. Mix the cabbage and onion into the mash and season as required.