Mix the butter, sugar and eggs together. Mix the flour with cocoa and baking soda and stir into the dough. Finally add the sour cream. Spread the dough on a baking sheet lined with baking paper and bake at 180 degrees for about 30 minutes (chopstick test). The cooled cake can be dusted with icing sugar or covered with a chocolate icing as desired.
I am also happy to bake leftover chopped up chocolate Santa Clauses and Easter bunnies. Simply add the chocolate chips to the batter after the sour cream.