Remove and discard skin from ham. Using a boning knife, score fat on ham 1/8" deep in a diamond pattern. Place ham, fat side up, on a lightly greased rack in a shallow roasting pan. Insert a meat thermometer, making sure it does not touch fat or bone.
Stir together preserves, mustard, and 1 cup peach nectar in a large bowl; pour over ham.
Bake ham, uncovered, at 350° for 2 hours and 20 minutes or until meat thermometer registers 140°, basting with pan juices every 20 minutes.
Transfer ham to a serving platter. Let stand 15 minutes before carving.
Pour pan drippings into a large saucepan. Add remaining 1 cup peach nectar; bring to a boil. Serve sauce with ham. Garnish, if desired.