1. Toast cinnamon and cloves in large saucepan over medium heat until fragrant, about 3 minutes. Add 4 cups cider and bring to boil. Pour spiced cider into large stockpot or clean bucket, add 4 cups cider and ice, and stir until melted.
2. Meanwhile, remove skin from exterior of ham and trim fat to ¼-inch thickness. Using sharp knife, cut slits spaced 1 inch apart in crosshatch pattern in surface layer of fat, being careful to cut down to, but not into, meat. Transfer ham to container with chilled cider mixture (liquid should nearly cover ham) and refrigerate for at least 4 hours or up to 12 hours.
3. Discard cider mixture and transfer ham to large oven bag. Add 1 cup fresh cider to bag, tie securely, and cut 4 slits in top of bag. Transfer to large roasting pan and let stand at room temperature for 1½ hours.
4. Adjust oven rack to lowest position and heat oven to 300 degrees. Bake until ham registers 100 degrees, 1½ to 2½ hours. Meanwhile, bring remaining 4 cups cider and mustard to boil in saucepan. Reduce heat to medium-low and simmer, stirring often, until mixture is very thick and reduced to ⅓ cup, about 1 hour.
5. Combine sugar and pepper in bowl. Remove ham from oven and let rest for 5 minutes. Increase oven temperature to 400 degrees. Roll back oven bag and brush ham with reduced cider mixture. Using your fingers, carefully press sugar mixture onto exterior of ham. Return to oven and bake until dark brown and caramelized, about 20 minutes. Transfer ham to carving board, tent with aluminum foil, and let rest for 15 minutes. Carve and serve.