How to Make It
Heat oven to 350° F. In a small bowl, mix together the butter and garlic.
In a large roasting pan, place the carrots, 1 of the onions, and 1 cup water; place a roasting rack in the pan. Season the turkey cavity with ½ teaspoon each salt and pepper and stuff with the remaining onion. Tie the legs together with twine and tuck the wings underneath the body. Place the turkey on the rack, rub with the butter mixture, and season with 2 teaspoons salt and ½ teaspoon pepper.
Roast the turkey, basting every 30 minutes with the pan juices, until a thermometer inserted in the thickest part of a thigh registers 165° F, 2½ to 3 hours. (As soon as the garlic begins to brown, tent the bird loosely with foil; add 1 cup water to the pan if the vegetables begin to scorch.)
Carefully tilt the turkey to empty the juices from the cavity into the pan. Transfer the turkey to a cutting board, tent loosely with foil, and let rest for at least 30 minutes and up to 1 hour before carving. Reserve the pan and its contents for the Giblet Gravy.