To make finely ground nuts, place husked toasted hazelnuts into food processor and process until finely ground. See my note below the recipe about how to husk hazelnuts once they are toasted (between your two hands – it’s very easy and effective)
In a large mixing bowl, beat butter and sugar until creamy, then add ½ cup finely ground hazelnuts and vanilla and beat to combine. In a separate bowl, combine flour and salt, then add mixed flour and salt to the creamy butter-sugar mixture. Do not overmix, mix just enough to combine all ingredients and form a cookie batter.
Shape dough into 4 logs of different thickness (to make cookies of different radius – large and small). Wrap each log in plastic wrap and put wrapped cookie dough in the freezer for 30 minutes, then in the refrigerator for 30 minutes.
Preheat oven to 325 F. After cookie dough has been in the freezer and refrigerator, unwrap plastic and slice each log into thin cookie slices. Place cookie slices on ungreased baking sheet, spacing 1 inch apart. Bake for about 20 minutes, don’t let the cookies to get brown. After 20 minutes of baking, transfer cookies to rack to cool.
To decorate cookies, melt chocolate in a small skillet over medium heat, just until chocolate melts, about 5 minutes. Remove from heat.
Using spatula, brush half of the cookie on one side only (no chocolate on the bottom of the cookie) and along the cookie side. Transfer to rack to dry. Do that with each cookie (if desired). Then you can dip the chocolate side of the cookie into coarsely chopped hazelnuts. Return to rack. You can leave some cookies just covered with chocolate, without hazelnuts crumbs. You can also leave some cookies just plain (no chocolate, no hazelnuts on top of chocolate). Repeat with remaining cookies. Let cookies dry on rack for at least 1 hour, for chocolate to harden.
Notes
Note: The recipe also calls for toasted and husked hazelnuts, which is pretty easy to do. I preheated oven to 350, placed raw hazelnuts (with skins still on) on the baking sheet and toasted them for 5-10 minutes. After I took the hazelnuts out of the oven and after they cooled off, I husked them by rubbing a handful of hazelnuts between my hands. This did a pretty good job of getting rid of most of the skins.Recipe adapted from Epicurious.