For the streetcars, knead all ingredients by hand or in a food processor to a shortcrust pastry, wrap in cling film and chill in the fridge for approx. 2-3 hours.
For the marzipan mixture, mix marzipan, powdered sugar, and egg whites and stir until smooth and pour into a piping bag with a serrated nozzle. On a floured work surface, roll out the dough into strips about 5mm thick and 4cm wide.
Using a piping bag with a smooth nozzle, pipe 2 strips at a time along the edge of the shortbread dough. Bake briefly in the preheated oven at 160 °C hot air for about 7 minutes, remove and fill the still hot edges with hot jam.
Bake again for 2 minutes and then cut with a pastry wheel into pieces about 4 cm wide.