Break the dark chocolate into pieces and place it in a bowl with the butter. Melt gently in a bain-marie.
In another bowl, whisk the eggs with the brown sugar, vanilla sugar and spices. Mix well until the eggs are foamy.
Pour the chocolate-butter mixture over the beaten eggs, stirring constantly.
Add the flour as well as the yeast and cocoa, then mix again.
Cover and refrigerate for 1 hour so the dough hardens and is easier to handle.
Preheat your oven to 180°C.
Form 25 small balls between your hands then roll them in the icing sugar, in a deep plate. Place them on a baking sheet covered with parchment paper.
Bake for 10 minutes then let cool on a rack.
