1 can sweetened condensed milk (label removed)
1. In a large pot, fill with water to cover the can of sweetened condensed milk. Over high heat, bring to a boil Let simmer for 2 1/2 to 3 hours, making sure to add more water as necessary. Remove the can of dulce de leche from the water and let cool to room temperature.
2. Preheat oven to 350˙F. In a medium bowl combine flour and salt. In a stand-up mixer cream together butter and sugar for 3-4 minutes, mixture will turn light and fluffy. As mixer is going, add in flour and mix until combined. Shape into a disc, wrap in plastic and refrigerate for 30 minutes.
3. On a heavily floured surface, roll out the dough to 1/2-inch thickness. The dough will be a little sticky so be sure to flour your roller, too. Using a 1 1/2-inch round cutter, cut out shortbread cookies and place on baking sheet. Poke a series of three holes, using a fork, in the center of each cookie.
4. Transfer cookies to oven and bake for 12-15 minutes, or until edges are slightly golden brown. Let cool on wire rack. To assemble the sandwiches, open the can of dulce de lece. Lay half of the shortbread cookies bottom-side up. Spread about 1/2 teaspoon of dulce de leche on one half of the cookies. Top with the other half and lightly press down until you’ve gone through all the cookies.
Yields approximately 25 sandwich cookies.