In a large bowl, combine base ingredients. Mix until crumbly. Reserve 2 cups for topping and press remaining crumbs into a sprayed 13x9 pan.
In a large bowl, blend all filling ingredients. Beat at highest mixer speed until smooth and creamy.
Pour filling over crust. Sprinkle with reserved crumbs. Bake at 350 degrees for 45 to 55 minutes or until firm when pan is lightly shaken.
Cool and cut into 36 bars. Store in refrigerator.
High altitude -- Above 3500 feet, add 3 tbls. flour to the dry cake mix in base. Add 1 tbls. water to filling before mixing. Bake at 375 degrees for 40 to 45 minutes.
Flavor combinations are endless -- Dark Chocolate Cake Mix with Buttercream Frosting; Yellow Cake Mix with Chocolate Frosting; Carrot or Pumpkin Cake Mix with Cream Cheese Frosting; Lemon Cake Mix with Lemon Frosting, etc., etc. You can also add 1/4 to 1/2 cup of peanut butter to vanilla frosting for a peanut butter filling. Mini chocolate chips can also be added to the filling.