Dice the cold butter into small cubes. Combine with sugar, hazelnuts, and flour. Mix quickly for 1-2 minutes until just combined; do not overwork the dough.
Shape the dough into a roll, place in a freezer bag, and refrigerate for 1 hour.
Roll out the dough to the thickness of a finger, cut into sticks the size of a pencil, and place on a baking sheet lined with baking paper.
If the dough has become warm during rolling, return it to the refrigerator for 15-20 minutes before baking.
Bake at 150°C (302°F) for 25 minutes until lightly golden.
Allow to cool for 5 minutes, then dip one end in melted couverture and let set for 10 minutes.