Make 1/4-inch-deep cuts in ham; rub ham with salt and pepper, and place, fat side up, in a roasting pan. Stud onion with cloves, and place in pan with celery and garlic.
Bake at 325° for 3 to 3 1/2 hours or until a meat thermometer inserted into the thickest portion registers 160° (about 20 minutes per pound), basting with wine. Remove ham from pan. Skim fat from drippings.
Whisk together drippings, broth, brandy, and flour in a saucepan. Cook over medium heat 5 minutes or until thickened. Serve with ham.