• Preheat oven to 350ºF. Line an 8x8 metal baking pan with parchment paper so that it hangs over the edges for easy removal. Spray with nonstick spray.
• Make the cheesecake filling. In a mixing bowl, use a hand mixer to mix the cream cheese, sugar, and sour cream until the filling is smooth and no lumps remain. Mix in the egg and vanilla until smooth and set aside.
• Melt the chocolate. In a small saucepan, combine the butter, oil, and chopped bittersweet chocolate. Melt over medium-low heat, stirring occasionally, until all the chocolate is melted. Whisk in the cocoa powder and set aside to cool slightly.
• Mix the dry ingredients. In a small bowl, whisk together the flour, baking powder, and salt.
• Whip the eggs and sugar. In a medium mixing bowl, combine the eggs, sugar, and brown sugar. Use a hand mixer to whip for 3-4 minutes on high speed until light and fluffy.
• Finish the brownie mix. Whisk in the cooled butter and chocolate mixture into the whipped eggs and sugar until smooth. Switch to a rubber spatula and fold in the dry ingredients until no streaks of flour remain. Set aside 2/3 cup of brownie batter in a small bowl. Fold in the chocolate chips to the larger bowl of brownie batter.
• Marble the brownies. Spread the brownie batter in an even layer in the prepared pan. Top with the cheesecake filling and spread in an even layer. Dot the reserved brownie batter over the top of the cheesecake mixture then use a knife or toothpick to create swirls.
• Bake. Transfer to the oven for 35-40 minutes, until the cheesecake topping is slightly puffed. Let the cheesecake brownies cool to room temperature. Then, refrigerate for 1 hour before serving.

Storage Instructions

• To store: I actually like storing them in the fridge so that the cheesecake is cold, but you can also store them at room temperature. Store the brownies in an airtight container at room temperature for 1 day, or refrigerated for 3-5 days.

  To freeze: Cheesecake brownies can be wrapped in plastic wrap and then placed in a freezer-safe ziplock bag and frozen for up to 3 months. The combination of plastic wrap and a ziplock bag helps prevent freezer burn. Let the brownies defrost overnight in the fridge before serving.