Combine the first 7 ingredients (through pepper) in a medium bowl. Mix well, and set aside.
Position a rack on second-lowest level in oven; preheat to 500°. Have a large roasting pan ready with a rack set in pan.
Put 1/2 cup vegetable mixture inside neck cavity and 1/2 cup inside chest cavity of turkey. Scatter remaining vegetables on bottom of pan, and add 1 cup water. Truss turkey by tying ends of legs with twine. Lift wing tips up and over back; tuck under bird. Using a pastry brush, brush turkey with 1/2 of the melted butter. Place turkey, breast side down, on roasting rack. Roast 30 minutes; turn oven down to 350°. Baste turkey with pan juices; roast 30 minutes more.
Remove turkey from oven. Carefully (using something to protect your hands) turn turkey breast side up. (It won't be very hot at this point.) Baste with pan juices and remaining butter; return to oven. If breast is becoming too dark, shield with foil. Roast, basting with pan juices again after 45 minutes. Turkey is done when an instant-read thermometer registers 165°F when inserted into thickest part of a thigh away from the bone.
Tilt juices from cavity into pan. Transfer bird to a carving board, and cover loosely with foil. Let rest for 30-40 minutes before carving. Carve turkey, and serve.