1. Preheat oven to 325oF. Line an 8x8 baking pan with parchment paper. Let the paper hang over the sides to easily remove the brownies. Spray with cooking spray.
2. Melt the butter in a medium saucepan. Add sugar, cocoa, and salt. Mix until combined.
3. Remove from heat and add vanilla. Add eggs one at a time, mixing until incorporated before adding the next.
4. Gently fold in flour.
5. Pour the brownie batter into the bottom of the prepared pan. Set aside and make the cheesecake filling.
6. Using an electric mixer, beat cream cheese until completely smooth. Add sugar, vanilla, and egg and beat until smooth.
7. Drop spoonfuls of cheesecake filling over brownie batter. Use a knife to swirl through. Scatter candy bar pieces over the batter.
8. Bake for 20 to 30 minutes, or until cheesecake is set. Let cool completely at room temperature. Transfer to refrigerator and chill for at least 2 hours, preferably overnight.