Preheat oven to 350 degrees F. Line 2 baking sheets with parchment paper.
Prepare the hazelnuts: toast hazelnuts in a baking sheet for about 10 minutes, until the skin starts to crack and smells toasty. Let them cool slightly and peel off the skin by rubbing the hazelnuts with a clean kitchen towel. Once peeled off, pulse the hazelnuts in a food processor until finely ground.
In a medium bowl, mix the flour with the ground hazelnuts and salt. Set aside.
In a bowl of a stand mixer, mix butter and sugar on medium-low until smooth, about 2-3 minutes. Add flour mixture and mix to combine, until just incorporated. Do not overmix. Note: you can use a hand mixer too, or do it by hand.
Dump the dough on top of some plastic wrap. Roll dough to 1/2 inch disk, with plastic wrap on top so it’s easy to roll. Wrap and chill at least 1 hour.
Roll out chilled dough to 1/4 inch thick. Cut out cookies with your favorite cookie cutter. I used a 2 1/2 inch fluted round cookie cutter. Place them on the prepared baking sheets.
Cover with parchment paper and chill in the refrigerator for 30 minutes.
Bake at 350 degrees F for 8-10 minutes. Let cool completely.
Pipe in chocolate hazelnut spread, and sandwich the cookies. Dust with confectioners sugar using a sifter or strainer.