Preheat Oven:

Preheat oven to 350°F (175°C). Grease a 9-inch springform pan and line the bottom with parchment paper.

Make Brownies:

In a medium bowl, whisk together melted butter, sugar, eggs, and vanilla. Stir in cocoa, flour, salt, and baking powder until just combined. Pour into a greased 8×8-inch pan and bake 15–18 minutes until a toothpick comes out with a few moist crumbs. Cool completely and cut into small cubes.

Prepare Cheesecake:

In a large bowl, beat cream cheese and sugar until smooth. Add eggs one at a time, then mix in vanilla, sour cream, and heavy cream until creamy and well combined.

Assemble:

Gently fold half of the brownie cubes into the cheesecake batter. Pour batter into prepared springform pan and scatter remaining brownie cubes on top, pressing lightly into the batter.

Bake Cheesecake:

Bake at 350°F (175°C) for 45–55 minutes, or until the edges are set and the center is slightly jiggly. Turn off oven and leave cheesecake in oven with door ajar for 1 hour to prevent cracking.

Cool and Chill:

Remove from oven and cool to room temperature. Refrigerate for at least 4 hours, preferably overnight.

Serve:

Remove from springform pan, slice, and serve. Optional: drizzle with chocolate sauce or top with whipped cream.