Preheat oven to 350°F (175°C) and prepare a springform pan.
In a bowl, mix melted butter, sugar, eggs, and vanilla extract.
Stir in cocoa powder, flour, and salt until just combined.
Pour brownie batter into the pan and spread evenly.
Bake for 15–20 minutes until slightly set.
In another bowl, beat cream cheese until smooth.
Add sugar, eggs, vanilla, and sour cream, mixing until creamy.
Pour cheesecake mixture over the brownie layer and smooth the top.
Bake for 35–40 minutes until the center is just set.
Cool at room temperature, then refrigerate for at least 4 hours or overnight before serving.