Preheat oven to 350°.
Combine the cake mix, egg and 8 tablespoons butter and mix well with an electric mixer. Pat the mixture into the bottom of a lightly greased 13 by 9-inch baking pan.
In a large bowl, beat the cream cheese until smooth. Add the eggs, vanilla and 8 tablespoons butter and beat together.
Next, add the powdered sugar and mix well. Spread over cake batter and bake for 40 to 50 minutes. Make sure not to over bake as the center should be a little gooey.