Remove giblets and neck from turkey; place in refrigerator for use in gravy, if desired. Rinse turkey with cold water; pat dry with paper towels.
Place turkey, breast side up, on a rack in a lightly greased roasting pan. Lift wing tips up and over back, and tuck under bird.
Combine butter and next 4 ingredients in a small bowl; rub 2 Tbsp. seasoned butter inside turkey cavity.
Place onion, celery, and garlic inside turkey cavity. Rub remaining 4 Tbsp. seasoned butter all over outside of turkey, legs and all. Tie ends of legs together with heavy string, or tuck under flap of skin around tail.
Bake, uncovered, at 325 for 2 1/2 to 3 hours or until a meat thermometer inserted into the meaty part of thigh registers 17
Shield turkey with aluminum foil towards end of cooking, if necessary, to prevent overbrowning.
Transfer turkey to a serving platter, reserving pan drippings for Bourbon Gravy.
Let turkey stand, covered with foil, at least 15 minutes before carving.