In a large bowl or mixer, cream the softened butter and sugar until light and fluffy. Add the vanilla extract and mix well. If using, add the lemon zest for extra flavor.
Combine the ground nuts, flour, cinnamon, and salt in a separate bowl.
Gradually add the dry ingredients to the butter mixture, blending until a soft dough forms.
Divide the dough in half, shape each portion into a disk, and wrap them in plastic wrap. Refrigerate for at least 1 hour or until firm.
Preheat your oven to 350°F (180°C).
Using a rolling pin (I prefer French style rolling pin) on a lightly floured surface, roll the dough out to about 1/8 inch thickness.
Cut out the dough using a round 2- inch round biscuit cutter or cookie cutter. Cut out a circle (or shape) in the centers in half of the rounds. You can use a small cookie cutter like a heart or star. These cookies with the cut-outs will serve as the "tops" of your Linzer cookies. The remaining complete rounds will serve as the "bottoms."
Place the cookies on parchment paper lined on a prepared baking sheet.
Bake for 10-12 minutes or until the edges are lightly golden brown. Be cautious not to overbake.
Allow the cookies to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.
Once the cookies are completely cooled, dust all the tops of the cookies with powdered sugar.
Spoon a small amount (about one teaspoon) of preserves onto each base.
Gently press the cutout tops onto the preserves, creating a sandwich effect.
Enjoy your hard work and the most beautiful Linzer cookie.