Preheat oven to 325°F (160°C). Remove giblets and neck from turkey cavity. Rinse turkey inside and out and pat dry with paper towels.
In a small bowl, combine softened butter, poultry seasoning, salt, and pepper. Rub mixture all over the turkey skin.
Place quartered onion, chopped celery, carrots, and crushed garlic cloves inside the turkey cavity.
Place turkey in a roasting pan and cook for approximately 15 minutes per pound, or until a meat thermometer inserted into the thickest part of the thigh registers 165°F (74°C).
Let the turkey rest for at least 20 minutes before carving.
Notes
For extra flavor, consider brining the turkey overnight before roasting. Basting the turkey with pan juices every 30 minutes during cooking can also help keep it moist.