Melt the black chocolate and margarine in a pan on low heat. Beat the eggs with the powdered sugar until frothy. Add the chocolate and margarine mixture to the powdered sugar mixture and stir well. Add the vanilla sugar, flour and walnuts and mix well again.
Line a baking sheet with baking paper, distribute the mixture on top and bake in the middle of the oven for 25 minutes.
Take out of the oven, turn out onto a handkerchief and cut into slices.