Melt the butter and let it cool down. Mix oat flakes, flour, sugar, eggs and butter with the whisk of the mixer. Cover and chill for about 30 minutes.
Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Line two baking trays with baking paper. Place approx. 9 teaspoonfuls of dough heaps on each baking tray at a large distance and press them into flat circles.
Bake in a hot oven for about 10 minutes one after the other. Take out, let it cool down for about 5 minutes and remove from the baking tray together with the baking paper. Let it cool down. From the remaining dough bake other cookies in the same way and let them cool down.
Bake a total of about 44 biscuits.
Coarsely chop the chocolate coating and melt in a hot water bath. Allow to cool a little, then spread half of the biscuits with 1 tbsp. chocolate coating each. Place the remaining biscuits on top and press down lightly. Pull the cookie edges all around the couverture and let them dry.