Mix the butter, sugar, vanilla sugar and eggs until creamy. Stir in the flour, espresso or espresso powder mixed with baking powder and the nuts. Finally add the chocolate chips.
Spread the dough on a baking sheet and bake light brown: with hot air 160 ° C, approx. 30 min. For the icing, stir the icing sugar with espresso and liqueur until smooth and spread on the slightly warm cake.