The hens may be prepared up to 2 hours ahead and refrigerated until ready to roast.
Prepare:
Preheat the oven to 450°F.
Have ready:
Being careful not to tear it, loosen the skin around the breast and thighs, then force the butter under the skin with your fingertips. Rub any remaining butter on the outside of the bird. Place it breast side down on a V rack in a roasting pan and roast for 20 minutes. Reduce the oven temperature to 350°F and turn the bird breast side up. Add to the pan, if desired:
Roast until the internal temperature of the thickest part of the thigh reaches 165°F and the juices from the thigh run clear when the skin is pierced, 25 to 30 minutes more. Transfer to a cutting board, cover loosely with foil, and let stand for 10 minutes before carving. Carve the bird and pour the pan juices over the meat.