To make the crust generously spray a jellyroll pan with Pam. With an electric mixer, blend dry cake mix, melted butter, and 1 egg on low speed until moistened. Mix on medium speed for 2 minutes, and pat onto bottom and side of the jellyroll pan, set aside.
To make the filling mix 3 1/3 cups powdered sugar, eggs, vanilla, and cream cheese until ingredients are moistened. Carefully cover the mixer with a large, clean kitchen towel. Turn mixer on high for 5 minutes. Turn mixer to low speed and remove towel.
Add remaining 1 1/2 cups powdered sugar and mix until well blended. Replace the towel and return mixer to high speed, and beat for an additional 5 minutes. Pour mixture over crust in pan and spread evenly. Bake at 350 degrees for 40 minutes, or until golden brown. When cool, slice into squares.