To make this cake a "chocolate butter cake" : I skip the powdered sugar, reduce the flour to 200g ( 1 3/4 cups), add 50g or 1/2 cup dutch cocoa (it must be dutch process or it can mess with the chemistry of the cake) and use vanilla greek yogurt instead of sour cream, and add two more tablespoons of it (for a total of 3/4 plus 2 tablespoons of yogurt). You can also add half a cup of chocolate chips!