Roasted marmalade ham

INGREDIENTS

• 3-4 kg middle cut higher-welfare gammon with the knuckle left on
• 2 carrots, roughly chopped
• 2 sticks celery, roughly chopped
• 2 bay leaves
• 16 black peppercorns
• 1 piece leek, for the bouquet garni
• 1 piece celery, for the bouquet garni
• 1 bay leaf, for the bouquet garni
• 1 sprig fresh thyme
• 2 oranges
• 2 tablespoons sea salt
• 3 tablespoons freshly ground black pepper
• 1 jar thin-rind marmalade
• 1 handful fresh rosemary, leaves picked