Using a food processor or a hand mixer, blend sugar with butter, vanilla, salt, hazelnut flour, and almond flour. Fold in egg whites and mix until uniform.
Using a spoon, create circles with approximately two tablespoons (30 milliliters) of batter on a parchment paper-covered baking sheet, leaving five centimeters of space between cookies. Bake for ten minutes, or until slightly browned around edges.
Remove from oven and carefully remove hot cookies from tray with a spatula, then drape over a rolling pin or a wine bottle to create a curve in the cookie. Wait until cookies cool before serving alongside Crema di Cogne (see recipe).