Preheat oven to 325°F. Line a 9×9″ pan with foil and spray with non-stick cooking spray. Set aside.
In a large bowl, add the brownie mix, butter, buttermilk, vanilla, egg and 1/2 cup chocolate chips. Stir for 2 minutes, or until smooth. Add a Tablespoon or two more of milk if needed to thin the batter.
In a medium bowl, add the cream cheese, sugar, egg and vanilla. Mix with an electric mixer until smooth and creamy. Refrigerate for 10 minute if gets too thin.
Place half of the brownie batter in the pan and then spread the cream cheese mixture evenly on top. Then add 9 scoops of the brownie batter on top of cream cheese filling. Swirl with a knife to create a marble effect. Top with the remaining 1/4 cup chocolate chips.
Bake cheesecake brownies for 35-45 minutes, or until a toothpick comes clean. Remove from the oven and allow to set for at least 30 minutes before cutting. Remove foil from pan then slice.
Enjoy with a cold glass of milk! :)
Instead of adding chocolate chips, feel free to use brownie mix with chocolate chips already included. I use a plastic knife to cut my brownies. Make sure they have cooled at least 30 minutes before cutting.