Hardly adapted from Paula Austin via myrecipes.com
1 cup (2 sticks) unsalted butter, room temperature
½ cup white sugar
2 large egg yolks
1 large egg
2 teaspoons pure vanilla extract
2 shy-cups all-purpose flour
1 cup cornstarch
1 teaspoon baking powder
½ teaspoon kosher salt
About 2 cups dulce de leche or caramel sauce*
Optional powdered sugar or sweetened flaked dried coconut
* For the perfect consistency of dulce de leche filling, I mixed a Chilean dulce de leche in a can, which is very, very thick, with a much thinner Mexican dulce de vaca in a plastic jar. Canned dulce de leche will invariably be thicker, so buy a thin and a thick dulce de leche to mix together. Also, I tend to like the very dark dulce de leche, because of the richer flavor.
1. In the bowl of a stand mixer fitted with a paddle attachment, beat the butter and sugar on medium speed until smooth. Add the egg yolks, egg, and vanilla, beating until combined.
2. In a medium bowl, mix together the 2 cups flours, cornstarch, salt, and baking powder. Add to the butter mixture in small increments, beating until blended. Divide the dough in half, pressing each half into a disk, wrap the disks in plastic and the freeze until firm, about 30 minutes.
3. Preheat oven to 350 degrees. Unwrap dough on a lightly floured surface. Rolling one disk at a time to 1/8 of an inch thickness. Cut out 2-3 inch diameter rounds, placing about one inch apart on a buttered baking sheet. Bake for about 10 minutes, or until the cookies just begin to turn golden brown. Let cool completely on a cooling rack.
4. To make sandwiches, spread about 1 tablespoon of the mixed dulce de leche on a cookie, then top with another cookie, twisting to spread the filling. Roll the sides in coconut or dust with powdered sugar if desired.