Heavily butter a 15-in. x 10-in. x 1-in. pan; set aside. Heavily butter a large bowl; set aside. In a stand mixer, beat egg whites until stiff peaks form. In a heavy saucepan over medium heat, combine the sugar, corn syrup and water. Cook and stir until sugar is dissolved and mixture cones to a boil, about 10 minutes. If sugar crystals are present, cover and boil for 1-2 minutes to allow steam to wash crystals down. Cook, without stirring, until a candy thermometer reads 238° (soft ball stage), about 6-8 minutes. With mixer running carefully and slowly add hot liquid in a steady stream over egg whites. Beat 10 minutes longer.
