Wash the chicken pieces, then pat them dry. Place the chicken in a deep glass or nonporous glazed bowl. Add the sherry, cover, and let sit overnight, or longer, in the refrigerator. When ready to cook, remove the sherried chicken from the refrigerator, and drain, reserving the sherry.
Put half the butter into a large, heavy casserole and melt it over moderate heat. Add the chicken, a fe