To bake: Preheat the oven to 325° F / 165° C / gas mark 3. Line a shallow roasting pan with foil and place the ham in it, cut side down. To grill: Preheat the grill. Lightly grease the bottom of a foil pan and place the ham in it, cut side down.
Using a paring knife, score the ham's fat (not the meat) in a diamond-shaped pattern. This helps the flavor soak through to the meat and provides a decorative look. Insert whole cloves into the center of the diamonds if desired.
In a small saucepan, combine the glaze ingredients and bring to a boil over medium heat. Remove from heat and set aside.
Add 1/2 cup of water to the roasting pan and cover the pan and ham tightly with foil, crimping tightly at the pan's edges. Bake (or grill over indirect heat) for 30 minutes.
Remove the foil covering and baste the ham with the glaze. Resume baking or grilling. Baste every 10 minutes until the ham has reached an internal temperature of 140°F / 60°C (approximately 30 minutes). Allow the ham to rest at room temperature for 10 minutes before serving.