Position a rack in the lowest position of the oven and preheat to 325 degrees F.
Reserve the turkey neck and giblets to use in gravy or stock. Rinse the turkey inside and out with cold water. Pat the turkey skin dry. Turn the turkey on its breast. Loosely fill the neck cavity with stuffing. Using a thin wooden or metal skewer, pin the neck skin to the back. Fold the turkey's wings akimbo behind the back or tie to the body with kitchen string. Loosely fill the large body cavity with stuffing. Place any remaining stuffing in a lightly buttered casserole, cover and refrigerate to bake as a side dish. Place the drumsticks in the hock lock or tie together with kitchen string.
Place the turkey, breast side up, on a rack in the roasting pan. Rub all over with the softened butter. Season with salt and pepper. Tightly cover the breast area with aluminum foil. Pour 2 cups of the turkey stock into the bottom of the pan.
Roast the turkey, basting all over every 30 minutes with the juices on the bottom of the pan (lift up the foil to reach the breast area), until a meat thermometer inserted in the meaty part of the thigh (but not touching the bone) reads 180 degrees and the stuffing is at least 160 degrees, about 4 1/2 hours. Whenever the drippings evaporate, add stock to moisten them, about 1 1/2 cups at a time. Remove the foil during the last hour to allow the skin to brown.
Transfer the turkey to a large serving platter and let it stand for at least 20 minutes before carving. Increase the oven temperature to 350 degrees F. Drizzle 1/2 cup turkey stock over the stuffing in the casserole, cover, and bake until heated through, about 30 minutes.
Meanwhile, pour the drippings from the roasting pan into a heatproof glass bowl or large measuring cup. Let stand for 5 minutes, then skim off and reserve the clear yellow fat that has risen to the top. Measure 3/4 cup fat, adding melted butter if needed. Add enough turkey stock to the skimmed drippings to make 8 cups total.
Place the roasting pan on two stove burners over low heat and add the turkey fat. Whisk in the flour, scraping up browned bits on the bottom of the pan, and cook until lightly browned, about 2 minutes. Whisk in the turkey stock and the optional bourbon. Cook, whisking often, until the gravy has thickened and no trace of raw flour remains, about 5 minutes. Transfer the gravy to a warmed gravy boat. Carve the turkey and serve the gravy and the stuffing alongside