Preheat your oven to 325°F (163°C).

In a large mixing bowl, melt the butter and mix with brown sugar and granulated sugar until creamy.

Add eggs one at a time, mixing thoroughly after each addition, then stir in vanilla extract.

In a separate bowl, whisk together cocoa powder, flour, baking powder, and salt. Gradually mix into the wet ingredients until combined.

Pour the brownie batter into the prepared springform pan and bake for 20-25 minutes until just set.

In a mixing bowl, beat together cream cheese, sugar, sour cream, and cocoa powder until smooth.

Add eggs one at a time, mixing on low speed until combined, then stir in flour.

Pour the cheesecake batter over the warm brownie layer, smoothing the top.

Bake for 50-60 minutes until the edges are set and the center jiggles slightly.

Cool the cheesecake in the oven for 1 hour, then refrigerate for at least 4 hours or overnight.

Slice and serve, optionally topped with chocolate ganache or fresh berries.