How to Make It
Heat oven to 325° F. Spread the hazelnuts on a rimmed baking sheet and toast in oven, tossing occasionally, until fragrant, 10 to 12 minutes.
Rub the warm nuts between 2 clean dish towels to remove the skins. (Discard the skins.) Process in a food processor until finely ground.
Beat the butter, vanilla, salt, and 1/2 cup of the sugar in a bowl with an electric mixer on medium-high until light and fluffy, 2 to 3 minutes. Beat in the ground nuts. Reduce mixer speed to low and gradually add the flour; stir until just combined. Chill for 1 hour and up to 2 days.
Line 2 baking sheets with parchment.
Place the remaining cup of sugar in a bowl. Roll level tablespoonfuls of the dough into balls and place on the baking sheets, spacing them 2 inches apart.
Bake, rotating the sheets halfway through, until the edges are firm and pale golden brown, 16 to 18 minutes. Let cool slightly on the baking sheets, then toss the warm cookies in the sugar to coat; transfer to a wire rack to cool completely.