Separate the egg. Knead together the flour, butter, sugar, hazelnuts and the egg yolk.
Put the dough in the refrigerator for about 30 minutes.
Then roll out the dough and cut it into strips – about 7 cm long and 1 to 3cm wide, depending on your preference. Place on a prepared baking sheet. Beat the egg whites with the powdered sugar until stiff and put them in a piping bag. Decorate the nut bars with it.
Bake in a preheated oven at 180°C for about 20 minutes.
Makes about 45 pieces.