Insert a knife into either end of the ham, next to the bone, making 3"-deep incisions in each end. Fill the incisions and rub the outside of the ham with salt. Collect and reserve any salt that doesn't cling to the ham; store in a container in refrigerator. Place ham in a nonreactive pan and cover with plastic wrap, then aluminum foil; let chill.
Turn ham every 1–2 days, rerubbing with remaining salt, for 7 days. (Pour off any juice that collects in the pan.) Wash the ham under cold running water; be sure to flush out the salted incisions. Transfer ham to a large, clean container and cover with cold water; let chill overnight. Drain.
Preheat oven to 325°. Bake ham on a rack in a roasting pan, covered, for 1 hour. Uncover, increase oven temperature to 375°, and continue to bake, basting from time to time, until the meat pulls away from the bone, about 3 hours more. (Cover ham loosely with a piece of aluminum foil if skin is browning too fast.) Set ham aside to let rest a little, then carve and serve.