In a food processor fitted with a metal blade, process hazelnuts and sugar until finely ground. Add butter and process until well-mixed, then add salt and flour and process until dough comes together in a ball. Transfer to a sheet of wax paper, roll into a log about 1-1/2 inches in diameter, about 12 inches long. Chill for at least one hour, up to overnight.
Preheat oven to 325 degrees. Slice dough into 1/2-inch slices and place on parchment-lined baking sheet. Bake until lightly golden around the edges, about 8 to 10 minutes.
Makes 2 dozen
Recipe used with permission from Janine MacLachlan, The Rustic Kitchen cooking school, www.rustickitchen.com.