Beat butter, sugar, vanillin sugar, salt, orange zest and egg whites until fluffy. Then stir in the flour.
Divide the dough in half and mix one half with the cocoa powder. Form each of the light and dark dough into rolls and place together in a piping bag fitted with a large star nozzle. Pipe S-shaped loops onto a prepared baking sheet.
Bake in a preheated oven at 200°C for about 10 minutes.
Half decorate the cooled cookies with melted chocolate icing.
