Heat oven to 325°F.* Carefully peel paper-like skin from around bulbs of garlic, leaving just enough to hold garlic cloves together. Cut 1/4 to 1/2 inch from top of bulb to expose cloves. Place cut side up on 12-inch square of aluminum foil. Drizzle bulb with oil. Wrap securely in foil. Place in pie plate or shallow baking pan. Roast 45 to 60 minutes, or until garlic is tender when pierced with toothpick or fork. Cool slightly. Squeeze garlic into bowl; mash with fork.
After removing turkey from roasting pan, pour drippings (turkey juices and fat) into bowl or glass measuring cup, leaving brown bits in pan. Let drippings stand about 5 minutes to allow fat to rise. Skim 6 tablespoons fat from top of drippings, and return to pan; discard any remaining fat. Add enough broth or water to remaining drippings to measure 3 cups; reserve.
Stir mashed garlic and flour into fat in pan, using wire whisk. Cook over medium heat about 1 minute, stirring constantly and scraping up brown bits, until mixture is smooth and bubbly. Remove from heat.
Gradually stir in reserved 3 cups drippings; increase heat to medium-high. Heat to boiling, stirring constantly. Boil and stir about 1 minute or until gravy thickens. Stir in salt and pepper.