Preheat oven to 350 degrees. Spray a 13 x 9 baking dish with non-stick spray.

Crust: Place the cake mix, butter, and egg in a large mixing bowl. Blend on low for 2 minutes. Scrape down the sides of the bowl and mix into the batter. The batter should begin to form a ball. Using your fingers, pat the batter evenly over the bottom of the baking dish. Set aside.

Filling: In the same mixing bowl, beat the cream cheese until fluffy. Add eggs, vanilla, and melted butter. Beat for 1 minute. Add the confectioners sugar a little at a time and beat until all of the sugar is mixed well. Set aside.

In a saucepan over low heat melt chocolate. Measure out 1 cup of the cream cheese filling and stir into the melted chocolate. Stir well. Set aside.

Pour the remaining filling over the crust, making sure to cover the entire surface. Using a spoon, drop the chocolate batter over the top of the filling. Using a knife, swirl the two batters together, making a marbled effect. Be careful not to cut through the crust.

Bake the cake for about 45 minutes or until it is browned, and the center still jiggles when you shake it slightly. Remove from the oven and cool about 20-30 minutes. Cut into bars.

Serve warm or cold from the refrigerator. To store: Cover and store in the refrigerator for up to a week. It does not last that long at my house. :) Note: The cake will crack as it bakes. This is normal.