Preheat the oven to 325 degrees. Grease a 16-cup bundt or tube pan and dust with flour. Set aside.
Beat the butter and sugar in the bowl of a mixer fitted with the paddle attachment for 7 minutes, until light and fluffy. Scrape down the sides of the bowl with a spatula. Add the cream cheese and beat until smooth. Add the eggs, one at a time, beating well after each addition and scraping down the sides of the bowl as needed. Add the sour cream, vanilla, salt, and coffee powder (if using) and mix to combine.
Sift the flour, cocoa powder, and baking powder into a bowl. Turn mixer speed to low and add the flour mixture, beating just until combined. Scrape down the sides of the bowl and fold batter with a spatula to ensure homogeneousness.
Spoon the batter into the prepared pan, smooth the top, and bake for 70-80 minutes, until a cake tester comes out clean. When the cake is done, let cool for 10 minutes on a wire rack. Invert the cake from the pan onto the rack, then invert again to top side up. Let it cool completely on the wire rack. Dust with confectioners' sugar. Serve with vanilla ice cream or whipped cream.
