Take the giblets out of the turkey. Remove any excess fat and leftover pinfeathers and pat the outside dry. Season the whole turkey with kosher salt and black pepper. Tie the legs together with string and tuck the wing tips under the body of the turkey.
When ready to cook, set the temperature to 275℉ and preheat, lid closed for 15 minutes.
Place turkey on the grill and roast for 3-4 hours. Check the internal temperature, the desired temperature is 160℉ in the thigh next to the bone. Remove the turkey and set the temperature to 450℉, baste the turkey all over with butter while waiting on the grill to increase then place back on the grill and cook for an additional 20 minutes to finish cooking through the meat and crisp the skin. Let rest for 15-20 minutes before carving.