Preheat oven to 350 degrees.
Put the butter and sugar in a bowl and whip it in a mixer for 3 minutes.
Add flour, ground cardamom, baking powder and salt gradually. Use your hand to mix the cookie dough.
Take a small piece of dough the size of a walnut. Shape the cookie into a ball and place a piece of hazelnut in the middle.
Arrange all on a pan lined with parchment paper. Bake for 20 minutes.
Wait until cold, spread Nutella® on one piece and cover it with another piece.