Mix cocoa, flour, baking powder and cinnamon and pass through a sieve. Stir butter until creamy. Stir in the egg first, then the icing sugar and vanillin sugar. Add the flour mixture and knead into the fat mixture with the dough hooks of the hand mixer. Press dough flat, wrap in foil and refrigerate for about 1 hour. Knead the dough again and form approx. 45 small balls. Place on 2 baking trays lined with baking paper.
Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 10 minutes. Remove and let cool on a cake rack. In the meantime, finely chop the couverture and melt over a warm water bath. Pour the couverture into a piping bag, cut off the tip. Decorate cookies with it. Allow to set and dust half with cocoa
waiting time approx. 1 1/2 hours