Preheat the oven to 350°F (175°C).
Grease a 9-inch springform pan.
Melt the butter and mix in granulated sugar.
Add eggs one at a time, whisking after each addition.
Stir in flour, cocoa powder, and salt until just combined.
Pour the brownie batter into the prepared pan and bake for 25 minutes.
Beat the cream cheese until smooth.
Add powdered sugar, vanilla extract, and sour cream; mix until creamy.
Pour the cheesecake batter on top of the brownie layer.
Bake for an additional 30-35 minutes until set.
Let cool and refrigerate for at least 4 hours before serving.