Preheat oven to 350 degrees
Line a 13 by 9-inch baking pan with foil, allowing ends to hang over edges. Brush with cooking spray
In a large bowl, microwave chocolate and butter for 2 minutes, or until butter is melted. Stir until chocolate is melted. Allow to cool slightly (3-4 minutes)
Stir in sugar; add eggs and vanilla. Add flour and stir until combined.
Spread into prepared pan.
In a mixing bowl, beat cream cheese until smooth. Add sugar, egg and flour and mix until blended.
Drop spoonfuls of cheesecake batter over brownie batter (you may have extra cheesecake batter). Swirl with a knife.
Bake for 30-40 minutes until a toothpick inserted into center comes out clean.
Cool pan on wire rack. When cool, use foil to lift from pan and transfer to cutting board to slice with a knife dipped in hot water.