Combine first 4 ingredients in bottom of a shallow roasting pan coated with cooking spray. Remove and discard giblets and neck from turkey. Rinse the turkey with cold water; pat dry. Trim excess fat.
Starting at neck cavity, loosen skin from breast and drumsticks by inserting fingers and gently pushing between skin and meat. Lift wing tips up and over back; tuck under turkey.
Combine cheese, 1/4 cup sage, butter, minced garlic, 3/4 teaspoon salt, and 1/4 teaspoon pepper; rub mixture under the loosened skin and over breast and drumsticks. Rub turkey skin with cut sides of lemon halves; squeeze juice into turkey cavity. Place lemon halves in turkey cavity; tie legs together with kitchen string.
Place turkey, breast side up, on vegetable mixture in pan. Bake at 425°F for 30 minutes, and pour 2 cups broth over turkey. Tent turkey breast loosely with foil. Bake an additional 30 minutes.
Reduce oven temperature to 325° (do not remove turkey from oven). Bake at 325°F for 1 1/2 hours or until a thermometer inserted into meaty part of thigh registers 180°F, basting every 30 minutes. Remove turkey from pan. Cover and let stand 30 minutes; discard skin.
Place a large zip-top plastic bag inside a 4-cup glass measure. Pour drippings through a sieve into bag; discard solids. Let drippings stand 10 minutes (fat will rise to the top). Seal bag, carefully snip off 1 bottom corner of bag. Drain drippings into a medium bowl, stopping before fat layer reaches opening; discard fat. Add enough of remaining chicken broth to drippings to equal 3 cups.
Heat a medium saucepan over medium-high heat. Coat pan with cooking spray. Add shallots; sauté 1 minute. Add sherry; bring to a boil. Cook until reduced to 1/2 cup (about 54 minutes). Stir in remaining 1 tablespoon sage, and cook for 30 seconds. Add reserved drippings; bring to a boil.
Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour and water, stirring well with a whisk. Stir flour mixture into drippings mixture; bring to a boil. Cook 2 minutes or until thickened, stirring constantly. Stir in remaining 1/4 teaspoon salt and remaining 1/4 teaspoon pepper. Serve gravy with turkey.
Serving size approx 5 oz turkey, 3 tablespoons gravy.
Chef note: For a beautiful garnish, roast lemon halves and peeled shallots at 425°F for 20 minutes; arrange with fresh sage springs on the turkey platter.