For the dough, stir the butter with the powdered sugar, vanilla sugar and a pinch of salt until creamy. Stir in the egg yolks. Add flour and desiccated coconut and work everything into a smooth dough. Put the dough wrapped in foil in the fridge for 1 hour.
Shape the dough into small balls and place them on the baking sheet with a little space. Make indentations in the center of the ball with a floured wooden spoon handle.
Bake in the preheated oven at 175 degrees for between 10 and 12 minutes.
When the biscuits are ready, place them on a wire rack and let cool down well. Then carefully melt the chocolate in a water bath. Using a teaspoon, pour the melted chocolate into the hollows of the coconut balls.