Mix the egg with the sugar and the vanilla sugar packet with a wooden spoon. Add the flour, salt, butter cut in cubes and knead with your fingers. Form a ball and reserve in the refrigerator 1 h. Preheat the oven to 180 ° C (item 6).
On a floured work surface, spread out the dough and cut out shapes of your choice with a cookie cutter. Fry half of the shortbreads with a smaller cookie cutter. Bake for about 10 minutes.
Pour the jam into a saucepan and cook for 5 minutes to make it a bit sticky. Once the shortbreads are cool, put 1 tbsp. coffee jam in the center of a solid shortbread and cover with a perforated shortbread.