Sieve the flour onto a work surface. Press a depression into it. Add the sour cream. Put cold fat in flakes, sugar, vanillin sugar, salt, cinnamon and lemon peel on the flour rim.
Chop the ingredients with a wide knife. With cool hands quickly knead to a smooth dough. Cover and let cool for about 1 hour. Then roll out the dough between two layers of foil to a thickness of approx. 3 mm.
Cut out about 50 medium-sized hearts. Place them on a baking tray lined with baking paper. Mix egg yolk, sour cream, sugar and cinnamon. Spread half of the hearts with it. Bake everything in a preheated oven (electric: 200 °C/ gas: level 3) for 12-14 minutes until golden brown.
Let it cool down. Stir the jelly until smooth and apply to the uncoated biscuits. Place the remaining biscuits on top. Press down lightly.