1. Put ham in a very large container, such as a bucket, and cover with water. Let soak 3 days, changing water at least twice a day. Scrub with a stiff brush; rinse well.

2. Preheat oven to 350 degrees. Put ham in a large, deep, heavy roasting pan; transfer to oven. Add enough boiling water to come half-way up sides of ham. Cover with foil. Bake until an instant-read thermometer inserted in the thickest part registers 160 degrees, about 20 minutes per pound. Check occasionally to ensure cooking liquid is just simmering; adjust oven temperature as needed. Remove from oven; let cool in cooking liquid. Remove skin, leaving a small amount of fat on surface.

3. Preheat oven to 500 degrees. Place ham on a baking sheet lined with foil. Score fat in a crosshatch pattern, if desired. Cook sugar and vinegar in a small saucepan over medium heat, stirring occasionally, until sugar has dissolved. Spread over ham. Sprinkle with cornmeal. Bake 5 minutes. Remove from oven, and brush with glaze from pan. Bake until sugar has caramelized and is bubbling, 3 to 5 minutes more. Cut into very thin slices. Serve warm or at room temperature.