How to Make It
Melt butter in a small skillet over medium. Add salt, thyme, sage, pepper, and fennel seeds; cook, stirring often, until fragrant, about 1 minute. Remove from pan, and cool completely, about 10 minutes. Reserve 1 tablespoon of butter mixture.
Remove giblets and neck from turkey; reserve for another use. Pat turkey dry, and remove excess skin. Starting from neck, loosen and lift skin from turkey without completely detaching it. Spread butter mixture remaining in bowl evenly under skin. Carefully replace skin. Drizzle skin with oil, and rub with reserved 1 tablespoon butter mixture. Tie ends of legs together with kitchen twine; tuck wingtips under. Let stand at room temperature for 1 hour, or refrigerate 12 to 24 hours. (If refrigerated, let turkey stand at room temperature 1 hour before cooking.)
Preheat oven to 375°F. Place onions, carrots, celery, and bay leaves in bottom of a roasting pan; add a roasting rack. Coat rack with cooking spray. Place turkey on rack, and transfer to oven. Add water to pan. Bake in preheated oven until a meat thermometer inserted in thickest portion of thigh registers 165°F, about 1 hour and 45 minutes, rotating pan halfway (on same rack) after 55 minutes. Remove turkey from oven, and let stand at least 30 minutes.