Work the cornstarch, flour, cocoa, vanilla sugar, espresso powder and butter into a smooth dough. Shape the dough into 2 rolls (each approx. 15 cm long) and cover and chill for 1 hour.
Cut the rolls into 25 slices each. Wrap a hazelnut each with it and shape it into a ball. Place on baking sheets lined with baking paper and bake at 200 ° for 12-15 minutes. let cool down.
Melt the couverture and cake icing, mix gently and dip half of the balls in it. Place a chocolate mocha bean on each ball. let dry