2 large onions, chopped
2 celery ribs, chopped
1/2 pound fresh mushrooms, sliced
1/2 cup butter
1 (14.5 ounce) can chicken broth
1/3 cup minced fresh parsley
2 teaspoons rubbed sage
1 teaspoon salt
1 teaspoon poultry seasoning
1/2 teaspoon pepper
12 cups unseasoned stuffing cubes
Warm water
1 (14 pound) turkey
Melted butter

In a large skillet, saute the onions, celery and mushrooms in butter until tender. Add broth and seasonings; mix well. Place bread cubes in a large bowl; add mushroom mixture and toss to coat. Stir in enough warm water to reach desired moistness.
Just before baking, loosely stuff turkey. Place any remaining stuffing in a greased baking dish; cover and refrigerate until ready to bake. Skewer turkey openings; tie drumsticks together with kitchen string. Place breast side up on a rack in a roasting pan. Brush with melted butter.
Bake turkey, uncovered, at 325 degrees for 3-3/4 to 4-1/2 hours or until a meat thermometer reads 180 for the turkey and 165 for the stuffing, basting occasionally with pan drippings. (Cover loosely with foil if turkey browns too quickly.)
Bake additional stuffing, covered, for 30-40 minutes. Uncover; bake 10 minutes longer or until lightly browned. Cover turkey with foil and let stand for 20 minutes before removing stuffing and carving. If desired, thicken pan drippings for gravy. Yield: 12 servings (10 cups stuffing).

Source: allrecipes.com