Knead a shortcrust pastry from the dough ingredients. If the dough is too soft, you can add a little more flour. Roll out the well-worked dough on a floured work surface about 0.5 cm thick. Now, from the dough, rub out rectangles measuring 7 cm x 4 cm or - if you like it larger - also to 10 cm x 5 cm. For the filling, beat the egg white until stiff, gradually adding the vanilla sugar and sugar. Chop the prunes and stir into the egg whites with the remaining ingredients. Spread the filling over half of the rectangles, leaving some space at the edge. Then cover with the remaining rectangles and press down the edges of the dough well. The school bites are then placed on a baking sheet lined with baking paper. Bake in a preheated oven at 175 ° C for about 20 minutes. The school snacks keep fresh for a long time in a well-closing container and can be baked in advance.