1. Preheat the oven to 325°F (165°C). Remove the neck, giblets, and fat from the tail area and save for another use. Stuff the neck cavity loosely with stuffing, and pin the neck skin to the back with a skewer. Loosely fill the body cavity with stuffing and cover the exposed stuffing with foil. Using kitchen twine, tie the drumsticks together and secure the wings to the body.
2. Place the turkey on a rack in a roasting pan. Rub with the butter and season with salt and pepper. Loosely cover the breast area with foil. Add 2 cups water to the pan.
3. Roast, basting every hour or so (lifting the foil to do so), estimating about 15 minutes per pound, for about 3½ hours, until an instant-read thermometer inserted in the thickest part of the thigh, not allowing it to touch a bone, reads 175°F (79°C). During the last hour of cooking, remove the foil. Transfer the turkey to a platter. Let stand for 30 minutes.
4. Meanwhile, make the gravy. Pour the pan drippings into a glass bowl. Skim off and measure 6 tbsp fat; discard remaining fat. Add enough stock to degreased drippings to make 1 quart (1 liter).
5. Place the pan over medium heat. Add the fat, whisk in the flour, and let cook 1 minute. Whisk in the stock mixture and bourbon, if using, scraping up the browned bits, and bring to a boil. Simmer over low heat, whisking often, until thickened, about 10 minutes. Season with salt and pepper and pour into a sauceboat.
6. Carve the turkey and serve with the gravy.