1.Preheat oven to 350°. Slice ¼ inch off top of each garlic head. Place garlic, cut side up, in foil and drizzle with oil. Wrap garlic in foil to seal. Place on rimmed baking pan and roast 45 minutes. When cool enough to handle, squeeze out garlic into small bowl.
2.Increase heat to 400°. Mash garlic with 2 teaspoons Creole Seasoning, butter and rosemary. Remove neck and giblets from turkey and place in large heavy metal roasting pan; discard liver. Rinse turkey with cold running water; pat dry with paper towels. Work your fingers between the skin and breast to loosen skin. Evenly distribute garlic mixture under skin.
3.Sprinkle 3 tablespoons Creole Seasoning inside turkey cavity; fill cavity with some vegetables. Place any remaining vegetables in roasting pan. Place turkey, breast side up, on top of neck, giblets and vegetables. Rub turkey all over with remaining Creole Seasoning. Roast turkey 15 to 20 minutes or until outside of turkey is browned. Reduce heat to 325°. Roast 2 hours longer or until thermometer inserted into thickest part of thigh reads 160°, rotating turkey halfway through roasting time. Place turkey on large platter; cover with foil to keep warm. (Internal temperature will rise 5 to 10° upon standing.)
4.While turkey rests, prepare gravy: Skim excess fat from drippings in roasting pan. Place roasting pan on stovetop over medium-high heat. Add broth and simmer 10 minutes, stirring occasionally to loosen browned bits on bottom of pan. Remove and discard neck and giblets. In small bowl, whisk together water and cornstarch. Whisk cornstarch mixture into pan and heat to boiling. Boil 1 minute and remove from heat. Season with salt and pepper to taste.
