Separate eggs. Beat egg whites and 3 tbsp. water until stiff. Add sugar and vanilla sugar. Continue beating until the sugar has dissolved. Beat the egg yolks one after the other. Mix flour, ground nuts and baking powder and fold into the egg cream.
Line baking tray with baking paper. Pour the sponge mixture into a piping bag with perforated spout (approx. 7 mm Ø) and spray strips onto the baking tray. Chop the hazelnut leaves a little bit and sprinkle them on the sponge cake strips.
Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 10 minutes. Take out, let cool and dust with icing sugar.