Clean the turkey pat completely dry. The turkey must be at room temperature before you prepare and put in the oven.
Preheat oven to 325° F
Rub both sticks of salted butter all over the turkey in everything nook and cranny including the inside of the turkey cavity.
Add about 2-3 tbsp. of rubbed sage into 1 stick of the butter and as best you can shove the butter under the skin of the turkey.
Liberally season the turkey with kosher salt, pepper, and rubbed sage all over the outside , inside, and back of the turkey.
Add the Celery & onions into the turkey cavity and scatter all around the turkey roaster.
Cover loosely with aluminum foil and bake in the oven at 325° F for 20 minutes per lb.
Baste the turkey every 30-45 minutes. The turkey will brown under the foil, but uncover the last hour of roasting.
Remove the turkey at 165° internal temperature and let it rest until it rises to 170° before serving!