Add the butter and sugar into your baking bowl, and mix it for about 3 minutes in a food processor until you have an even mixture.
Add the egg and run the machine 2 more minutes.
Add the vanilla sugar, baking powder and flour, and continue to mix until you have a smooth and soft dough. If necessary, adjust with more flour if the dough is too sticky.
Cover the dough with plastic wrap and put it in the fridge for at least 1 hour, or overnight.
Roll out the dough until it becomes thin
Use cookie cutters to make heart shapes. On half of the hearts, cut out a small heart in the centre with a knife or a smaller cookie shape.
Place the hearts without holes on a baking tray lined with baking paper. Add a small teaspoon of jam in the middle of the hearts, then place the heart with the hole on top and gently squeeze the seams together.
Bake the biscuits in the middle of the oven at 190 degrees (top and bottom heat) for about 9 minutes. Let cool and share!