In a food processor, combine the flour and hazelnuts. Process until the hazelnuts and flour form a fine meal. Set aside.
In a large mixing bowl, beat the butter and 1/2 cup confectioners' sugar together on medium-high speed until smooth. Mix in the vanilla, espresso powder and salt until uniform. Add the flour/nut mixture and beat on medium speed until a dough forms. Form into a disk, wrap in plastic wrap and refrigerate for a minimum of 1 hour.
Preheat the oven to 350 degrees F.
Roll the dough into 1-tablespoon balls, place on a baking sheet and bake until the bottoms of the cookies are lightly browned, about 15 minutes. Let the cookies cool on the baking sheet for a few minutes.
Place the remaining confectioners' sugar in a bowl and gently coat the warm cookies once out of the oven. Place on a cooling rack to cool completely. Before serving, roll the room temperature cookies in the confectioners' sugar again to give them a nice, uniform appearance.
Recipe courtesy of Kristin Rosenau