1. Preheat oven to 175°C.
Using a blender, grind the hazelnuts to a fine powder and mix in a bowl with the flour, butter, salt and sugar until smooth.
Scoop out a little dough, shape into small rolls, taper the ends and bend the rolls into a crescent shape, then place on a sheet of parchment paper or silipat.
Bake for 15 minutes at 175°C, then cool completely.
When the cookies have completely cooled, melt the chocolate in a bain-marie, dip half the croissants in the melted chocolate and leave to set on a wire rack. Store in a metal box once the chocolate has hardened.