Mix egg and butter with powdered sugar and vanilla sugar until frothy. Scrape the pulp from the vanilla pod and add. Mix the potato flour and flour and stir into the batter alternately with the egg liqueur.
With a coffee spoon, place small heaps (diverge) on a baking tray lined with baking paper and bake for 10-12 minutes until the cookies are golden yellow.
Melt the couverture with palm oil in a water bath and coat half of the cookies with it. Leave the other cookies like that.