For glaze, combine the first six ingredients in a saucepan; bring to a boil, stirring constantly. Remove from the heat; set aside. Place ham on a rack in a shallow roasting pan. Score surface of the ham, making diamond shapes 1/2 in. deep. Spoon half of the glaze over ham. Cover and bake at 325° for 1-1/2 hours.
Remove drippings from pan and set aside. Return ham to pan. Bake, uncovered, 30 minutes longer or until a thermometer reads 140°, basting twice with remaining glaze.
Skim fat from ham drippings. In a saucepan, combine flour and 1/4 cup water until smooth. Stir in 3/4 cup drippings and remaining water (discard any remaining drippings). Bring to a boil; cook and stir for 2 minutes or until thickened.