Roughly chop the chocolate and melt it over a warm water bath, let it cool down a little. Put flour, cocoa, almonds, sugar, vanillin sugar, salt and egg yolk in a bowl. Add butter in pieces and liquid chocolate and knead with the dough hooks of the hand mixer to a smooth dough, wrap in foil and chill for about 1 hour. Shape the dough into croissants about 5 cm long and place them on 2 baking trays lined with baking paper. Bake the trays one after the other in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 10 minutes. Remove from the oven and let them cool down on cake racks.
Chop the white couverture and melt carefully over a warm water bath. With a small spoon, draw lines of couverture over a croissant half. Sprinkle with sugar pearls. Allow to dry and dust the other half with icing sugar. Store in a cool and dry place