• Preheat oven to 350°F. Line a 9x9-inch square pan with foil and spray with nonstick cooking spray.

Make the brownies

• Place chocolate and butter in a large microwave-safe bowl. Heat on high power in 30 second increments, stirring between each, until chocolate and butter are melted and smooth (about 2 minutes, depending on your microwave).
• Stir sugar and cocoa into chocolate and butter mixture using a spatula or wooden spoon. Stir in 3 eggs and vanilla, then stir in salt. Mixture will be grainy looking but smooth. Stir in flour carefully.
• Spread brownies in prepared pan and set aside.

Make the cheesecake

• Beat cream cheese with sour cream until smooth, then beat in 2 eggs, sugar and vanilla.
• Pour mixture over the top of the brownies in pan. Use a butter knife or a long skewer to swirl the brownies.
• Bake for 50-55 minutes, or until slightly puffed and no longer glossy (will be light golden around the edges of the foil). Cool completely at room temperature then chill for at least 4 hours before slicing and serving.
• Store in an airtight container for up to 3 days in the refrigerator or freeze for up to 3 months.