Mix espresso coffee with 11/2-2 tablespoons of hot water and let it cool down. Put flour, butter, sugar, egg yolk and espresso in a bowl. Knead first with the dough hooks of the hand mixer, then with your hands to a smooth shortcrust pastry.
Wrap in cling film and refrigerate for about 30 minutes. In the meantime, quarter the pistachios lengthwise and set aside. Roll out the shortcrust pastry thinly on a floured work surface and cut out fir trees with a mould (6-7 cm large).
Spread on 2 baking trays lined with baking paper. Bake one after the other in the preheated oven (electric oven: 200°C/ gas: level 3) for about 12 minutes. Let them cool down. Mix icing sugar and lemon juice to a smooth glaze.
Put them in a freezer bag, cut off a small corner and decorate the little trees with icing and pistachios. Leave to dry. Results in about 40 trees.