Remove turkey from brine, if using, and pat completely dry with paper towels. Let sit at room temperature for about 30 minutes.
Preheat the oven to 250 degrees. Place rack inside a roasting pan.
In a small dish, blend together salt, pepper, garlic powder, onion powder, paprika, sage, and thyme.
Rub turkey all over with softened butter or olive oil, including under the skin if desired.
Season the turkey with the spice blend. Be sure to season the cavity as well.
Stuff the cavity with onion, celery, garlic, and fresh rosemary.
Place turkey breast side up on the rack. Loosely cover with foil.
Roast at 250 degrees for about 30 minutes per pound, check internal temperature as it cooks.
During the last hour or so remove the foil so the skin can finish browning.
The turkey is done when the breast reaches 165 degrees and the thigh reaches 175 to 180 degrees.
Optional: For extra browning, increase oven temperature to 400 degrees for the final 10 to 15 minutes, watching closely.
Remove turkey from the oven, tent loosely with foil, and rest for at least 30 minutes before carving.