Separate eggs. Beat egg whites, sugar and espresso powder until frothy. Fold in ground nuts. Chill the dough for about 30 minutes. Then roll out between 2 layers of baking paper approx. 4 mm thick. Cut out circles (approx. 8 cm Ø) and place them on a baking tray lined with baking paper. Cut out one hole each (approx. 3 cm Ø).
Knead the dough again and process in the same way. Brush the circles with whisked egg yolk. Spread whole hazelnuts on top. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 10 minutes, let cool down. Chop the chocolate and melt on a hot water bath. Cover the biscuits with it. Decorate with gold leaf, let dry