In a large bowl, blend cake mix, water, egg substitute or egg white, vanilla extract and butter flavor on low speed until moistened. Beat on medium speed for 2 minutes. Pour batter into lightly greased and floured 13 * 9 inch pan. Bake at 350 degrees F for 25-30 minutes or until toothpick inserted in center comes out clean. Cool and cut into squares. Serve with little whipped topping and fresh fruit.