In a small bowl, combine the cream cheese, 1 egg, sugar and vanilla; set aside. In a large bowl, combine the cake mix, water, oil and remaining eggs. Beat on low speed for 30 seconds; beat on medium for 2 minutes.

Spray two 8 or 9" round baking pans with Pam baking spray. Pour half of the batter into each of the sprayed pans. Drop half of the cream cheese mixture by tablespoonfuls over the batter. Cut through batter with a knife to swirl the cream cheese mixture.

Bake at 350 F for 35-40 minutes or until a toothpick inserted near the center comes out clean (cake may crack). Cool on a wire rack.

In a large bowl, beat together the butter and cream cheese with an electric mixer. With the mixer on low speed, add the powdered sugar a cup at a time until smooth and creamy. Beat in the vanilla extract