For the dough, put flour, cocoa, baking powder, vanillin sugar, salt, sugar, egg, milk and butter in flakes in a mixing bowl. Knead with the dough hooks of the hand mixer to a smooth dough. Cover the dough and chill for about 30 minutes. Then roll out the dough on a well floured work surface. Cut out 3 locomotives (approx. 13 cm high and 6.5 cm long) with cookie cutters. Cut out 14 rectangles (14 x 6 cm) or several smaller rectangles from the remaining dough. Carefully place them on 2-3 baking trays lined with baking paper.
Bake the trays one after the other in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 12 minutes. Remove from the oven, place on a cake rack and allow to cool. Sift icing sugar. Mix icing sugar, egg white and lemon juice with the whisk of the hand mixer. Fill into a small freezer bag and cut off a small corner with sharp scissors. Decorate the locomotive and wagons with icing, sweets and sugar writing and dust with icing sugar