In a medium bowl, whisk together the cocoa powder, coffee, sour cream, and vanilla to make a shiny fudge. Set aside.
In the bowl of a stand mixer, beat the butter until smooth and shiny, about 2-3 minutes.
Add the granulated and brown sugars and continue beating until fluffy, and then beat in the eggs one at a time, mixing between each addition.
In a separate bowl, whisk together the flour, baking soda and salt.
Add the flour mixture to the butter mixture in thirds, alternating with the fudge mixture, scraping down the bowl several times as you go.
Pour the batter into prepared pan and bake for 30 mins.
A toothpick inserted into the center of the cake should come out clean when the cake is done.
If there’s batter on the toothpick, continue baking for a few minutes more until it comes out clean. Let the cake cool completely.