Soak the cheesecloth in the butter. Brush any remaining butter on top of the bird and cover the breast meat with the cheesecloth to keep it moist for the first part of cooking, tucking it into the natural crevices of the bird to keep it in place. Arrange the onions, garlic and carrots in the bottom of the pan and arrange the turkey on the roasting pan right above them. Place the pan in the center of the oven and roast for 20 minutes. Lower the oven to 350 F and count about 12 minutes per pound the turkey weighs. After about 2 hours, take the turkey out, gently remove the cheesecloth from the top of the breasts, baste the turkey with any pan juices, rotate the pan halfway and return to the oven. Place the turkey neck and the chicken stock in a medium pot and simmer gently on the stove as the turkey finishes cooking. Reduce the stock by about half.