Remove giblets and neck from turkey; discard. Rinse turkey with cold water; pat dry.
Loosen skin from turkey breast without totally detaching skin. Stir together 2 tablespoons butter, salt, and pepper. Rub butter mixture evenly over turkey breast under skin. Carefully place sage leaves and thyme sprigs evenly on each side of breast under skin. Replace skin.
Place pear halves, celery ribs, onion halves, and garlic cloves inside cavity. Place turkey, breast side up, on a lightly greased wire rack in an aluminum foil-lined shallow roasting pan. Rub entire turkey evenly with remaining 2 tablespoons butter.
Bake at 325° for 2 hours and 45 minutes to 3 hours and 30 minutes or until a meat thermometer inserted into thigh registers 180°, basting turkey every 30 minutes with pan drippings. (Prevent overcooking turkey by checking for doneness after 2 hours.) Remove turkey from roasting pan, and let stand 20 minutes before slicing. Garnish, if desired.
*1 (14-pound) whole fresh turkey may be substituted.