In a small bowl, combine butter with garlic and rosemary.
Rinse turkey inside and out with cold water; pat dry with paper towels.
Loosen the skin on the turkey by sliding your fingers underneath it, being careful not to tear it.
Rub a generous amount of the seasoned butter over the entire breast under the skin. Rub additional butter mixture over the entire outside of the turkey.
Place rosemary sprigs in cavity of the turkey and tie the legs together.
Place the bird on a rack in a roasting pan breast-side down. Add about a cup of water to the roasting pan. Roast turkey for 1 ½ hours.
Turn the turkey over so breast side is up and continue roasting until done (1 to 1½ hours), basting every 30 minutes.
The turkey is done when the thigh meat reaches an internal temperature of 175-180° F and the breast meat reaches an internal temperature of 165-170° F (Total roasting time approximately 3 hours). When the turkey is done, remove from the oven; let stand, loosely covered with foil for 20 to 30 minutes before carving.