Prepare the dough: In a medium bowl, whisk together the flour, cinnamon, and salt. In a separate large mixing bowl, beat the softened butter and sugar until light and fluffy — about 2-3 minutes. This creaming step gives your cookies that soft yet structured bite.

Add egg and vanilla: Mix in the egg and vanilla extract until fully incorporated. The batter may look slightly curdled at first, but keep mixing until smooth.

Combine dry and wet ingredients: Gradually add the flour mixture to the butter mixture. Stir until the dough comes together — it should be soft but not sticky. Wrap the dough in plastic wrap and refrigerate for at least 1 hour to let it firm up.

Roll and cut the cookies: Preheat your oven to 350°F (175°C). On a lightly floured surface, roll out the chilled dough to about ¼-inch thick. Use a round cookie cutter (or any shape you love) to cut out the cookies.

Bake: Place the cookies on a parchment-lined baking sheet and bake for 10–12 minutes or until the edges are just turning golden. Let them cool completely on a wire rack.

Fill with dulce de leche: Once the cookies are cool, spread about 1 tablespoon of dulce de leche on the flat side of one cookie. Top it with a second cookie to create a sandwich. Gently press to spread the filling to the edges.

Optional finish: Dust the tops with powdered sugar if desired. It gives a festive look and a hint of extra sweetness.