Easy White Cooked Icing

Cook water, sugar, corn syrup over low heat until mixture reaches 250 degrees on candy thermometer or until it spins a thread. Add marshmallows, beat into cooked mixture until mixed thoroughly. Pour this mixture over beaten egg whites; add vanilla and beat until thick enough to spread. You may mix coconut in icing or top each layer with coconut. Makes enough icing to frost 3 layers or large sheet cake.