Preheat Oven: Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper.

Make the Dough: In a medium bowl, whisk together flour, cinnamon, and salt. In a separate large bowl, cream together butter and granulated sugar until light and fluffy. Add the egg and vanilla extract and beat until combined. Gradually add the dry ingredients, mixing until a dough forms. Stir in ground almonds and lemon zest (if using).

Chill the Dough: Divide the dough into two discs, wrap in plastic wrap, and refrigerate for at least 30 minutes to firm up.

Roll and Cut: On a lightly floured surface, roll out one disc of dough to about ¼-inch thickness. Using a round cookie cutter, cut out cookies and place them on the prepared baking sheets. For half of the cookies, use a smaller cookie cutter to cut out a hole in the center (this will be the top of the sandwich).

Bake the Cookies: Bake for 8–10 minutes, or until the edges of the cookies are lightly golden. Let them cool on the baking sheets for a few minutes before transferring them to a wire rack to cool completely.

Assemble the Cookies: Once the cookies are cooled, spread about 1 teaspoon of dulce de leche on the whole cookies (the bottom half). Top with the cookies that have a hole in the center, pressing gently to form a sandwich.

Finish: Dust the top of the cookies with powdered sugar before serving.