Here is my tried and true method for how long to cook a 20-pound turkey. It is the best way to ensure your oven-roasted turkey is moist, juicy, & ready for the holidays. Whether you are hosting Thanksgiving, Christmas, or a party, all the guests will rave about this turkey.
Defrost your turkey for 3-5 days in the refrigerator.
If using a dry brine, start the salting process 3 days before cooking your turkey. Links above on the dry brine process I recommend.
Preheat the oven to 325°.
While the oven is preheating, prepare the turkey. Place the turkey in a roasting pan on a rack. Remove any parts in the cavity. Place the lemon and garlic pieces inside the turkey cavity.
Coat the skin of the turkey with softened butter. Next, combine all the spices in a small bowl. Sprinkle the turkey seasoning blend over the butter.
Place a large sheet of aluminum foil loosely over the turkey. Place it in the oven and cook for 2 hours.Baste only once during the first half of cooking, at about the hour mark.
Midway through the cooking, remove the foil and continue to cook another 2 - 2 ½ hours. Continue basting once every 30 minutes. Do not do it any more than that as the oven will lose heat.
To check for doneness, place an instant-read thermometer in the thickest part of the thigh. If it is 175°, the turkey is ready.
Remove the turkey carefully from the oven. Let it rest while covered loosely with foil for 30-60 minutes.
Place the turkey on a carving board or platter to serve. Remove the lemons and garlic from the cavity carefully and discard.