Yield: 19 cookies
Combine pecans, hazelnuts, flour, sugar, cinnamon, and salt in a food process. Pulse until nuts are roughly ground. Add softened butter and continue to process until dough forms.
Remove dough from food process and flatten into a disk. Cover with plastic wrap or place in an airtight container. Let chill in the fridge for one hour (up to overnight).
Preheat oven to 350° F. Portion chill dough into one tablespoon balls. Roll in powdered sugar and place on a parchment lined baking sheet, spacing cookies about 2 inches apart. Bake for 10-12 minutes until the tops of cookies are cracked. Allow to cool in baking sheet for 3 minutes before transferring to wire rack to cool completely. If desired, roll warm cookies in additional powdered sugar before serving.