1. In a bowl Whisk in the butter with the sugar.

2. Add an egg yolk, a pinch of vanilla and a pinch of salt, and whisk again.

3. Add the flour (make sure to keep a little bit of flour in case you are running low) and mix well till the mixture is soft and creamy.

4. Place the mixture in the refrigerator for 1 hour (or a bit more, but preferably not less).

5. Lay out a large piece of baking paper and sprinkle it with flour.

6. Empty the mixture over the baking paper and then gently spread it using your hands.

7. Sprinkle some flour on top of the now spread mixture.

8. Add a second sheet of baking paper over the mixture and then use a rolling pin to spread the mixture evenly between the two sheets of paper.

9. Remove the top sheet.

10. Using a spoon or knife, spread the hazel nut cream over the entire surface of the mixture, except the very edges of its 2 sides.

11. Using the lower sheet of baking paper to assist you, roll the dough into a roll, closing in the hazelnut cream, while making sure not to enclose the baking paper when rolling the dough.

12. Wrap the roll in some baking paper and then place it in the refrigerator for about 45 minutes.

13. Remove the dough from the refrigerator and unwrap it. Use a sharp knife and cut the dough into disc shaped biscuits (index finger thickness).

14. Place some non sticky baking paper on a baking pan, line the cut pieces on it and slightly press them down with your palm while always allowing some distance between each piece.

15. Bake at 180 degrees (air baking) for 10 minutes.

16. After you remove the pan from the oven, allow time for the cookies to cool down completely.

17. You can store them in a sealed container.