For the dough, knead butter in pieces, icing sugar, 1 pinch of salt, 250 g flour, vanilla flavouring and egg first with the dough hooks of the mixer, then briefly with your hands to a smooth dough. Wrap in foil and chill for about 30 minutes.
Line two baking trays with baking paper. Preheat the oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Roll out the dough on a lightly floured work surface to a thickness of approx. 4 mm. Cut out approx. 30 hearts (each approx. 6 cm Ø).
Use a small heart cutter (approx. 1.5 cm Ø) to cut out the middle of each heart. Knead, roll out and cut out the dough again and again until the dough is used up. Place the hearts on the baking trays.
Bake one after the other in a hot oven for 12-15 minutes and let them cool down.
For the icing, sieve icing sugar into a bowl. Stir with red syrup to a smooth, slightly thicker glaze. Spread the hearts with it and let them dry.