- In a medium mixing bowl, combine flour, baking powder, cinnamon, and salt. Whisk together to mix.
- In a food processor, pulse the hazelnuts until finely ground. Add the hazelnuts to the flour mixture. Whisk together to mix. Set aside.
- In a large bowl of an electric mixer, combine butter and sugar; cream together until mixture appears light and fluffy. Scrape down the sides and bottom of the bowl with a rubber spatula so the mixture blends evenly. Add egg yolks, vanilla, and lemon zest; beat until thoroughly mixed. Add flour mixture; stir until well mixed.
- Form dough into a 6 inch flattened disk and wrap in plastic wrap. Refrigerate until well chilled, 1 to 2 hours.
- Preheat oven to 350 degrees F. Baking sheets may be ungreased, lined with parchment paper, or lined with a non-stick baking mat.
- On a lightly floured pastry mat or pastry board, and using a lightly floured rolling pin, roll the dough to a ⅛ inch thickness. Cut dough with a round 2½ inch scalloped cookie cutter that has been dipped in flour (to help prevent dough from sticking to the cutter.) Cut out the center from half of the shapes with a 1½ inch scalloped cookie cutter. Re-roll the scraps, or bake the 1½ inch shapes separately.
- Bake: Place cutout dough 2 inches apart on baking sheets. Bake 11 to 13 minutes or until cookies are set and the edges are very lightly browned. Remove cookies from baking sheets with a metal spatula and place on a wire cooling rack to cool.