Preheat oven to 350°F (175°C). Grease a 9-inch (23 cm) springform pan.
In a medium bowl, combine the flour, cocoa powder, baking powder, and salt. Set aside.
In a large bowl, cream the butter and 1 cup of granulated sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla extract.
Add the dry ingredients to the butter mixture and mix until just combined. Spread the batter into the prepared pan and bake for 25 minutes, or until a toothpick inserted into the center comes out clean.
In a medium bowl, beat the cream cheese until smooth. Add the sour cream, 1/4 cup of sugar, and cocoa powder. Mix until well combined.
Spread the cream cheese mixture over the cake and bake for an additional 25 minutes. Allow the cake to cool completely before serving.
Interesting Facts
Cream cheese is a type of cheese that originated in the U.S. in the late 1800s.
Cocoa powder is made from cocoa beans that are roasted, ground, and processed into a powder.
Dark chocolate is made from cocoa solids and is richer in flavor than milk chocolate.