Cup of Yum
1. In a medium bowl, whisk together the cornstarch, flour, baking powder, baking soda, cinnamon and salt. Set aside.
2. In a stand mixer using the paddle attachment, cream together the room temperature butter and sugar on medium for 4 minutes. Mixture should be light, fluffy and a pale yellow color.
3. Add the egg yolks, vanilla extract and lemon zest to the creamed butter and mix until just combined.
4. Reduce the speed to low and add the dry ingredients until combined. Scraping the bowl down if needed.
5. Scrape the dough out on a clean surface, divide in two and shape into two disks. Wrap with plastic wrap and refrigerate for 1 hour.
6. Preheat oven to 350°F. Line baking sheets with parchment paper or silicone mat.
7. Working with one dough disk at a time, place one dough disk on a lightly floured surface and roll out until it is ¼-inch thick. Use a 2-inch round or scalloped cookie cutter to cut cookies and transfer to a prepared baking sheet. Continue shaping, re-rolling, and cutting the dough with the remaining scraps and repeat with other disk of dough. I typically get 32 cookies.
8. Bake the cookies in batches for 12 minutes on the center rack, and edges get a golden brown color.
9. Let them cool completely on baking sheet before assembly.
10. Place 1 tablespoon of dulce de leche in the center on the bottom half of a cookie and sandwich another to the bottom of another cookie, lightly pressing down until dulce de leche reaches the edges. Continue this process until all the cookie sandwiches are assembled.

Optional Garnishes

Cup of Yum
1. Roll the sides of the cookie in a plate with shredded coconut if using, and or dust the tops with powdered sugar using a fine mesh strainer.