Preheat your oven to 350°F (175°C) and grease a 9-inch springform pan.
In a large bowl, melt the butter, then stir in both sugars until combined.
Add eggs one at a time, mixing well after each addition.
Mix in flour, cocoa powder, and vanilla until just combined.
Pour half of the brownie batter into the prepared springform pan and bake for 20 minutes.
While the brownies bake, prepare the cheesecake layer by beating cream cheese with sugar and sour cream.
Add in eggs one by one, mixing well after each addition.
Spread the cheesecake batter over the partially baked brownie layer and top with the remaining brownie batter.
Bake for another 30-35 minutes, until the center is set.
Allow the cheesecake to cool completely, then chill in the fridge for at least 4 hours or overnight.
Before serving, drizzle hot fudge sauce on top and add whipped cream.
