Preheat oven to 350 degrees F. Toast the nuts on a baking sheet for 8-10 minutes until fragrant. Cool completely, then add them to a food processor with ¼ cup of the sugar and process until finely ground.
Add the flour, salt, cinnamon, and ground nut mixture together in a bowl and whisk to combine.
In the bowl of a stand mixer fitted with a paddle attachment, beat the butter and remaining ½ cup of sugar until light and fluffy, about 2-3 minutes. Add the egg yolks, vanilla, and lemon zest, then beat again to combine.
Gradually add the flour/nut mixture, about ⅓ at a time, mixing just until combined.
Divide the dough into 4 pieces, and press each piece into a disc. Wrap tightly in plastic wrap and chill in the refrigerator for at least an hour or up to two days.
When ready to bake, preheat the oven to 350 degrees F and line baking sheets with parchment paper.
Roll out each disc of dough on a lightly floured surface, one at a time, until between ¼- and ⅙-inch thick. Cut out into shapes using 3-inch cookie cutters in star, heart, or circle shapes. Transfer to the prepared baking sheets, then use a smaller cookie cutter to cut out windows in half of the cookies. Repeat with the remaining dough, re-rolling scraps until all of the dough has been used. If the dough gets too soft, set it back in the fridge to chill for a bit to help the cookies keep their shape.
Bake for 10-12 minutes until the cookies are just beginning to turn a nice golden brown around the edges. I prefer these cookies crunchy since they will soften slightly when filled. Cool completely on a wire rack.
Dust the top halves of each cookie with powdered sugar, then spread the bottom halves with the fruit preserves or other filling. Sandwich the top and bottom halves together. You may want to carefully spoon a little additional jam into the window on the top, although I usually skip this. You should end up with about 24 completed cookies.
Store the finished cookies in an airtight container on the counter or in the fridge for 4-5 days, or freeze for longer storage (up to 2 months). If frozen, you may want to dust the tops of the cookies with powdered sugar again after thawing.