Position rack on the lowest shelf in the oven. Preheat oven to 325.
When ready to cook, remove the wrapping from the turkey. Remove the neck and giblets from the breast and neck cavities; if desired, use them to make turkey gravy or stock. Rinse turkey inside and out with cold water and pat dry. Lightly season the breast and neck cavities with salt and pepper.
If you will be stuffing the turkey, turn it on its breast and loosely fill the neck cavity with cool dressing. Pull skin over the neck cavity to close, and fold wings behind the back to secure the neck and skin in place. (Alternatively, secure neck skin with a metal skewer.) Loosely fill the breast cavity with cool dressing. Place any remaining dressing in a buttered baking dish; cover and refrigerate to bake as a side dish.
Place turkey, breast side up, on a flat rack in a shallow roasting pan. If using a standard meat thermometer, insert it deeply into the thickest part of the thigh next to the body but not touching the bone. Rub turkey skin with oil; season with salt and pepper. Pour stock and vermouth into the roasting pan. Roast the turkey, basting every 30 to 45 minutes with juices from the pan, until a meat thermometer registers 180 and juices run clear, not pink, when the thigh is pierced with a fork, about 3 hours. The dressing inside should register at least 160 in its center.
To ensure easier carving and more tender meat, transfer roasted turkey to a large, warm serving platter or carving board and let sit at least 20 minutes (or as long as 1 hour) before slicing. If you have stuffed the turkey, remove all the dressing before serving.
To prepare oven for baking dressing in separate baking dish, carefully move the rack to the center of the oven and increase oven temperature to 350. Follow the baking instructions for dressing recipe.
To make the gravy: Drain all but 6 tablespoons of fat from the pan. Place over medium heat. Add flour, whisking until smooth. Cook until the flour turns golden, about 2 minutes. Gradually stir in stock and bring to a boil, scraping up any brown bits from the bottom of the pan with a wire whisk. Reduce heat to low and cook, stirring occasionally, until slightly thickened, 2 to 3 minutes. Season with salt and pepper. Strain into a warmed sauceboat.
Serves 12 to 14