Knead butter in pieces, icing sugar, flour, egg yolk and 1 pinch of salt first with the dough hooks of the hand mixer, then with floured hands to a smooth dough. Wrap in foil and chill for about 30 minutes
3-4 Line baking trays with baking paper. Divide the dough into three. Roll out 1 piece of dough between 2 layers of baking paper approx. 2 mm thin. Cut out hearts with a large heart cutter (approx. 6 cm Ø), cut out 1 smaller heart (approx. 3 cm Ø) from each half of the cookies in the middle. Place whole hearts and hearts with hole on a baking tray. Knead the remainder with the 2nd third, roll out and process in the same way until approx. 20 whole hearts and 20 hearts with a hole are produced. Bake the trays one after the other in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 10 minutes
In the meantime, knead the remaining dough, roll out again between 2 layers of baking paper approx. 2 mm thin, cut out hearts with a small heart cutter (approx. 4 cm Ø), cut out 1 smaller heart (approx. 2 cm Ø) from each half of the cookies in the middle. Process in the same way as the large hearts (a total of approx. 20 whole hearts and 20 hearts with a hole). Bake the remaining hearts at the same temperature for approx. 10 minutes
Bring the jam to the boil in a pot, pour through a sieve, allow to cool for about 5 minutes. Dust the biscuits with a hole with icing sugar, put 1-2 tsp. jam on the remaining biscuits depending on size and cover with a dusted biscuit. Leave to cool for about 1 hour
waiting time approx. 1 1/2 hours