Mix flour, cocoa powder, icing sugar and salt. Separate the egg. Add egg yolk and butter in flakes. Knead first with the dough hooks of the hand mixer, then with your hands to a smooth dough. Cover and chill for about 1 hour. Roll out the dough on a floured work surface and cut out stars (5 cm Ø). Place on a baking tray lined with baking paper.
Beat the egg whites until stiff, sprinkle 50 g sugar on top. Fold in vinegar and 1 tablespoon grated coconut. Pour the mixture into a piping bag and squirt onto the stars. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for 8-10 minutes. Remove the cookies and let them cool down. Dust with icing sugar and sprinkle with remaining grated coconut
1 1/4 hours waiting time