Holiday roast turkey with old-fashioned corn bread stuffing

3 tablespoons butter or margarine
1 large yellow onion (chopped)
5 cups crumbled corn bread
5 cups toasted fresh bread crumbs
1 teaspoon baking powder
1 teaspoon poultry seasoning
1/4 teaspoon black pepper
3/4 cup lower-sodium chicken broth
1 large egg (lightly beaten)
1 fresh or frozen and thawed turkey (12 pounds)
1 tablespoon vegetable oil

1. In a medium-size saucepan, melt the butter over moderate heat. Add the onion and cook for 5 minutes or until tender. Remove from the heat. In a very large bowl, combine the corn bread, bread crumbs, baking powder, poultry seasoning, and pepper. Stir in the onion mixture. In a small bowl, whisk together broth and egg. Stir into the corn bread mixture. Toss to coat well.
2. Preheat oven to 325 F. Rinse turkey, drain and pat dry. Remove neck and giblets; set aside to make the Giblet Gravy. Stuff and truss turkey. Place, breast-side-up, on a rack in a large roasting pan. Brush with oil. Insert roasting thermometer in turkey thigh without touching bone. Spoon remaining stuffing into a lightly greased 2-quart casserole; cover and refrigerate.
3. Roast turkey for 3 to 3 1/2 hours or until thermometer registers 180?F, basting often and covering with foil to prevent overbrowning if necessary. Bake the covered casserole of stuffing alongside turkey during the last 30 minutes of roasting, adding an additional 2 to 3 tablespoons chicken broth if stuffing is dry. Let turkey stand for 15 to 20 minutes before carving.
4. Meanwhile, cook neck and giblets for giblet gravy. Reserve 2 tablespoons of the pan drippings from roast turkey for giblet gravy. Prepare gravy. Carve turkey, discarding skin. Serve turkey and dressing with gravy.