Rub salt and jerk seasoning into the lamb thoroughly.
Cover and marinate in fridge overnight.
Preheat oven to 180C/350F.
Roll up and tie the leg of lamb in three places to secure. Roast for 45minutes (medium rare) If using cutlets grill for 8-10minutes on both sides.
Roast the head of garlic for about 45minutes.
Crush the soft inside of garlic cloves into a saucepan.
Add all the other ingredients for the sauce and stir.
Bring to the boil, making sure the guava jelly has melted completely. Simmer and allow to reduce by half.
Allow the lamb to rest for 10minutes before carving. Slice the lamb and glaze with the warm sauce.
Serves 8 - 10