If using a frozen turkey, you need to thaw it completely in the refrigerator. Plan on 24 hours for every 5 pounds of turkey. My turkey was 15 pounds and it took 3 days.

Remove the giblets from the cavity of the turkey. Discard, or refrigerate them if you want to use them for gravy.

Pat the turkey dry with paper towels and transfer to a large roasting pan. Sprinkle about a third of the salt and pepper inside the cavity, then stuff the celery, carrots, and onion inside.

Rub olive oil on the entire surface of the bird, then sprinkle with the remaining salt and pepper. (You may need to use kitchen twine to tie the legs together if the vegetables won't stay inside the bird.)

Place the turkey breast-side down in the pan. Let it sit at room temperature while you preheat your oven to 400°. (Make sure your top rack is removed, and your remaining oven rack is on the bottom of the oven.)

Bake the turkey uncovered at 400 degrees for 30 minutes, then turn the heat down to 350°. Bake for another 2 hours.

Turn the heat down to 235° and bake for about 60-90 minutes, or until a meat thermometer inserted into the breast meat reads 165°. (The cook time may vary, pay attention to the internal temperature!)

Remove the turkey from the oven and tent with aluminum foil. Let the bird rest for at least 20 minutes before carving. Don't forget to save the pan drippings to make turkey gravy!