1. Preheat oven to 350 degree F. Lightly oil a shallow baking pan. Place ham, cut side down, on prepared pan and let stand at room temperature 1 hour. Whisk together sugar, garlic, and cumin until combined well. Score skin of ham in a crosshatch pattern and rub with spice mixture.
2. Bake in middle of oven until an instant-read thermometer inserted in center of ham (without touching bone) registers 140 degree F, about 2-1/2 hours. Cover ham loosely with foil and let stand while making sauce.
3. Whisk together mustard, cider, and maple syrup in a bowl, salt and pepper to taste. Transfer to a gravy boat.
4. Carve ham into 1/8-inch-thick slices and serve with sauce. Makes 8 to 10 servings.