Preheat oven to 375 degrees, with rack in lowest position. Line a large roasting pan with aluminum foil; place roasting rack in pan.
With a sharp knife, trim fat, leaving a 1/4-inch-thick layer. Lightly score fat in a diamond pattern (do not cut into meat). Place ham, fat side up, on rack; roast 1 hour.
Meanwhile, in a small saucepan, combine jam and mustard (they can be mixed and refrigerated up to 1 day ahead). Transfer 1/2 cup mixture to a small bowl to glaze ham. Set aside saucepan with remaining mixture.
After 1 hour, brush ham with glaze. Repeat every 15 minutes until brown and shiny, and an instant-read thermometer inserted in the thickest part, avoiding bone, registers 130 degrees, about 1 hour more (if glaze starts to burn, tent ham with buttered foil). Discard unused glaze. Remove ham from oven; cover loosely with buttered foil to keep warm. Temperature will then rise another 5 to 10 degrees.
Bring jam mixture in saucepan to a boil. Carve ham, reserving bone and 2 cups of meat for Split Pea Soup. Serve with sauce.