Heat oven to 375. Spray a 9" x 13" baking pan w/ cooking spray. In lg bowl, beat cake mix and butter, add 1 egg. Stir well. Press mix into bottom of baking pan.
In another lg bowl, beat cream cheese, powdered sugar and 2 eggs until creamy. Stir in vanilla. Pour mix over cake mix. bake 30 min, or until just set. Cool, cut into bars and serve w/ fresh strawberries.