Place oven rack in lowest position. Preheat oven to 325°F. Place roasting rack in shallow roasting pan. Mix butter, poultry seasoning, salt and pepper in small bowl.
Place turkey, breast-side up, in prepared pan. Rub 2 tablespoons butter mixture inside cavity of turkey. Stuff with onion and celery. Spread remaining butter mixture evenly over turkey and under skin. Cover loosely with heavy duty foil.
Roast 2 hours, adding an extra 15 minutes per pound for larger turkeys. Remove foil. Roast 1 hour longer or until internal temperature reaches 165°F (175° in thigh), basting occasionally with pan juices. Remove turkey from oven. Let stand 20 minutes. Transfer to platter or carving board and slice. Reserve pan juices to make gravy, such as our Perfect Turkey Gravy, or to serve with turkey.