Preheat oven to 350 degrees F.
Combine the cake mix, egg, and 8 TBL butter and mix well with an electric mixer. Press the mixture into the bottom of a lightly greased 9x13 baking pan.
In a large bowl, beat the cream cheese until smooth. Add the eggs, 8 TBL butter and vanilla 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.