Make several 1/2-inch slits on outside of lamb and insert garlic. Place lamb in a large shallow dish; pour Dijon vinaigrette over lamb. Cover and marinate 24 hours in a refrigerator, turning lamb occasionally.

Remove lamb from marinade, reserving marinade. Place lamb, fat side up, on a rack in a shallow roasting pan; insert meat thermometer, making sure it does not touch fat. Bake lamb at 350 degrees F for 1 hour and 45 minutes or until desired degree of doneness (rare 140F, medium 160F, and well-done 170F).

Transfer lamb to a serving platter, reserving drippings in pan; let stand 10 minutes befire carving.

Skim fat from pan dripppings. Measure renaining liquid, add reserved marinade and enough water to measure 1-1/4 cups. Pour into a saucepan.

Combine flour and 1/4 cup water, stirring well; add to pan drippings mixture. Add dry red wine and pepper. Cook over medium heat, stirring constantly, until gravy is thickened and bubbly. Serve with leg of lamb. Garnish with rosemary and red pepper, if desired. Yield: 8 to 10 servings.