Stir together first 7 ingredients in a saucepan over medium-high heat; bring to a boil, stirring constantly. Reduce heat to medium-low; simmer, stirring constantly, 5 minutes or until preserves are melted and mixture is blended. Pour half of plum preserve mixture into a microwave-safe bowl.

Trim excess fat on ham to 1/8-inch thickness. If desired, make long, shallow cuts (about 1/16-inch deep) over entire ham, forming diamond patterns. Place ham on a wire rack in an aluminum foil-lined roasting pan. Brush ham with a portion of plum preserve mixture in saucepan.

Bake ham, uncovered, at 350° on lower oven rack 1 hour and 30 minutes, basting with remaining plum preserve mixture in saucepan every 30 minutes. Loosely cover with aluminum foil, and bake 1 hour and 45 minutes or until a meat thermometer inserted into the thickest portion registers 140°, basting every 30 minutes. Let ham stand 15 minutes before slicing. Garnish, if desired.

Microwave plum preserve mixture in bowl at HIGH 1 minute or until thoroughly heated. Serve ham with warm mixture.