Knead butter in pieces, sweetness, 1 egg and 250 g flour first with the dough hooks, then briefly with your hands until smooth. Cover and chill for approx. 30 minutes.
Roll out the dough on a little flour to a thickness of about 3 mm and cut out about 90 hearts (about 5 cm Ø). Place on 3 baking trays lined with baking paper. Whisk 1 egg yolk and approx. 1 tbsp. water. Brush the hearts with it. Sprinkle the oat flakes over them and press lightly
Bake all hearts one after the other in the preheated oven (electric oven: 200 °C/circulating air: 175 °C/gas: level 3) for 8-10 minutes. Let them cool down
Break chocolate into pieces. Melt in a hot bain-marie with plate-grease. Let it cool down a little. Pour into a plastic bag. Cut off a small corner and decorate the hearts with chocolate strips. Leave to dry