Roll out frozen puff pastry. Cut out approx. 12 moons (approx. 5 cm) and place them on a baking tray lined with baking paper. Whisk the egg and brush the moons with it. Bake in a hot oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer) for 10-12 minutes. Let them cool down.