Beat the egg whites until stiff, allowing the sugar to trickle in. Beat to a firm consistency. Add the pistachios, almonds and flour. Line two baking trays with baking paper. Pour the dough into a piping bag with a perforated spout and squirt about 25 cookies onto each tray. Bake in a hot oven (electric cooker: 150 °C/ gas: level 1) for 20-25 minutes.
Dissolve the chocolate and let it cool down. Stir in liqueur, egg yolk, fat, sugar and almonds. Spread over about 25 biscuits. Cover with remaining biscuits. Decorate with dissolved chocolate and pistachios