A simple but delicious cake recipe:
Blend food processor on high speed until smooth. gradually fold in sugar and salt, mixing until combined. Gradually fold in eggs (each egg 1/2 min.). Combine flour and baking powder; fold in in batches on medium speed. Divide batter in half. Melt espresso powder in liqueur and stir into one half of dough along with cocoa. Cut chocolate into pea-sized pieces. Fill a 30cm loaf pan** (greased and dusted with flour or possibly lined with parchment paper) alternately with a tablespoon of light and dark batter, sprinkle a few chocolate pieces on each layer. Gently pull through with a fork to stew the dough a tiny bit.
Bake: Bake at 180 °C for 60 min (test with a stick!). Cool the cake in the pan for a few minutes, then turn out and cool completely on a broiler. Frosting: Melt the espresso powder in hot water and gradually add the powdered sugar. Brush the cake with it and pat dry.
I used a bar of Milka espresso chocolate (seasonal product) instead.
** Optionally fill into 6 mini rodon cake molds (double muffin size), then bake only about half an hour.