• Preheat oven to 350°F. Grease and line an 8x8-inch baking dish with parchment paper.

Make the brownie batter

• In a small saucepan, melt the butter and chocolate chips over medium-low heat, stirring until smooth. Remove from heat and whisk in the cocoa powder.
• In a mixing bowl, whisk together the granulated sugar, brown sugar, eggs, oil and vanilla extract until combined.
• Stir in the melted chocolate mixture.
• Mix in the salt, then add the flour and mix until just incorporated. Reserve 1/2 cup of the batter for the topping.

Make the cheesecake layer

• In a medium bowl, beat the cream cheese until smooth. Add sugar, vanilla extract and egg. Beat until fully incorporated.

Make the raspberry swirl

• Mash the raspberries in a small bowl with sugar and cornstarch until no white remains.
• Assemble. Spread the brownie batter (minus the reserved 1/2 cup) evenly into the prepared pan. Pour the cheesecake mixture over the brownie batter and spread into an even layer.
• Drop the reserved brownie batter in rough vertical lines across the cheesecake layer. Add the raspberry mixture between the brownie batter lines, leaving any excess liquid in the bowl. Use a skewer or knife to swirl horizontally across the lines to create a marbled effect. Top with extra chocolate chips and a few whole raspberries if desired.
• Bake for 38-42 minutes, or until the edges are set and the center has a slight jiggle.
• Cool the brownies completely in the pan, then refrigerate for at least 1 hour before removing from the pan and slicing.