For the Burgenländer slices, preheat the oven to 180 degrees top/bottom heat.
Cream butter, sugar and egg yolks. Stir in nuts, flour mixed with baking powder and milk. Spread on baking tray and bake.
In the meantime, whip the egg whites with water and sugar, spread on the baked nut mixture and put back into the hot oven until the whipped egg whites take on a light color.
Cover the Burgenländer wafers with chocolate icing.