Preheat oven to 350°F. Grease a 9-inch springform pan and line bottom with parchment paper.
Whisk together flour, 1/2 cup cocoa powder, baking powder, and salt in a medium bowl.
In another bowl, mix melted butter, granulated sugar, eggs, and vanilla until well combined.
Combine wet and dry ingredients until just mixed. Pour into prepared pan and spread evenly.
Bake brownie base for 25-30 minutes until center is nearly set but slightly jiggly. Cool completely on wire rack.
Melt chocolate and let cool to room temperature. Beat cream cheese until smooth and fluffy, about 3 minutes.
Add powdered sugar, remaining cocoa powder, sour cream, and espresso powder. Mix until well combined.
Pour in cooled melted chocolate and blend until uniform. Pour filling over cooled brownie base.
Smooth top with offset spatula. Refrigerate for at least 6 hours or overnight before serving.