1. Place the gammon in a large pot with the onion, carrot, bay leaf and orange juice, and cover with water. Bring to the boil, reduce the heat and simmer for 1 hour and 30 minutes (usually 30 minutes per 500g of meat). Let the meat cool in the cooking liquid for a further 20 minutes.
2. Preheat the oven to 200°C. Trim off the skin of the gammon as soon as it is manageable (keep the fat), then score the fat without cutting into the meat. Place the gammon in an ovenproof dish. Beat the char siu, honey, chilli, ginger, mustard and soy sauce together and glaze the top of the meat. Pour about 250ml of the cooking liquid into the bottom of the dish (this will prevent any glaze that drips from burning) and bake for about 40 minutes or until the glaze is golden-brown and caramelised. Baste occasionally.
3. Fry the pineapple slices on a griddle pan until they have lovely char lines on both sides. Add the fruit to the meat in the pan. Sprinkle a thin layer of castor sugar over the glaze and bake for the last 10–15 minutes – this makes the glaze glossy and crunchy. Let the meat rest for 15 minutes before carving.