Preheat your oven to 350. Lightly grease a 13x9 pan and set aside.
Mix together the cake mix, egg, and the first 8 tablespoons of butter. Use your handy dandy KitchenAid to combine. Pat the mixture into the bottom of your prepared pan.
In a separate bowl, beat the cream cheese until smooth. Add the eggs, vanilla, and remaining butter. Stir in the powdered sugar and stir until combined. Spread over your cake and bake 45 minutes.