Finely chop the chocolate. Grind the almonds. Put the egg white in a fat-free mixing bowl. Beat with the whisk of the hand mixer until stiff. Add sugar, vanillin sugar and lemon juice bit by bit and continue beating until the sugar is dissolved.
Carefully fold in almonds and chocolate. Spread the wafers on a baking tray. Use 2 teaspoons of egg foam mixture to place some on each wafer and decorate with a walnut half. Bake in the preheated oven (electric: 150 °C / gas: level 1) for about 35 minutes.
Let it rest on the baking tray for about 15 minutes. Carefully loosen with a pallet, place on a cake rack, cool for about 2 hours and leave to cool. Dust with cocoa. Makes about 22 pieces.