Beat the egg whites with the whisks of the hand mixer until stiff. Add sugar, vanillin sugar and salt. Add lemon juice and beat to a tough, firm mixture. Mix the flour and coconut flakes and carefully fold into the beaten egg white mixture. Pour the mixture in two portions into a piping bag with perforated spout (5 mm Ø) and squirt 100 small biscuits onto 2 baking trays lined with baking paper. Bake the trays one after the other in a preheated oven (electric cooker: 150 °C/ convection oven: 125 °C/ gas: stage 1) for 20-25 minutes.
Remove cookies from the oven, place them on a cake rack and let them cool down. Put 1/4 teaspoon of jam on each half of the cookies. Place the rest of the cookies on top as a lid. Let the cookies dry in a dry place for about 4 hours. Then sprinkle the biscuits with pistachios or turn the jam rim in pistachios