Allow turkey three days to thaw in the refrigerator prior to roasting. Preheat the oven to 325 F. Place rack in the lowest position of the oven. Remove turkey neck and giblets. Rinse turkey and pat dry with paper towels. Place turkey, breast-side up, on a rack in a roasting pan. If desired, loosely fill turkey cavity with stuffing. Rub skin with butter, then season with salt and pepper. Pour 2 cups of turkey stock into the roasting pan. Loosely tent turkey with aluminum foil. Roast turkey for 2 1/2 hours, basting with pan juices every 30 minutes. When drippings evaporate, add remaining stock to the pan, 1 to 2 cups at a time. Remove foil and continue roasting until a meat thermometer inserted in thickest part of thigh reads 165 F, about 1 1/2 hours more. Transfer turkey to a large serving platter. Let stand for 20 to 30 minutes before carving.