- Let the turkey stand at room temperature for 1 hour.
- Position a rack in the lower third of an oven and preheat to 425°F.
- Remove the giblets and neck, if included, and reserve for making gravy, if desired. Rinse the turkey inside and out with cold water and pat dry with paper towels. Trim off and discard excess fat.
- Place the onion, celery, thyme, bay leaf and 1 tablespoon of the sage in the body and neck cavities, then season with salt and pepper. With kitchen twine, truss the legs together. To secure the neck flap to the back, slide a long piece of string under the body, raise it up across the wings and tie the string snug against the center of the breast. Brush the turkey with half of the butter and sprinkle with the remaining 1 tablespoon sage, salt and pepper.
- Place the turkey, breast side down, on a rack in a large roasting pan and roast for 45 minutes, basting with some of the remaining butter after 25 minutes.
- Reduce the heat to 325°F and turn the turkey, breast side up. Continue roasting, basting with the remaining butter and pan juices every 15 to 20 minutes, until an instant-read thermometer inserted into the thickest part of the breast, away from the bone, registers 165°F, and inserted into the thigh registers 175°F.
- If the breast begins to cook too quickly, tent it loosely with aluminum foil. Total roasting time should be 3 to 3 3/4 hours.
- Transfer the turkey to a warmed platter, cover loosely with foil and let rest for about 20 minutes before carving.