Recipe Instructions:
100 grams (about 7 tablespoons) butter, soft
40 grams confectioners' sugar
75 grams cornstarch
75 grams all-purpose flour
4 tablespoons dulce de leche
Cream the soft butter together with the powdered sugar until the mixture is fluffy. If your butter is very soft already, this should take no more than a couple of minutes with a handheld mixer.
Whisk together the cornstarch and the all-purpose flour, then combine it with the butter and sugar using a large wooden spoon until the dough starts coming together into a ball.
Preheat the oven to 350° F (175° C) and line a sheet pan with parchment paper. Place the disk of dough on a floured surface, dust it with some extra flour, then carefully roll the dough out to a thickness of no more than 5 millimeters (about 1/8-inch thick).
Using a 5-centimeter (2-inch) round cookie cutter, cut out 24 cookies (you will have to re-roll the dough a couple of times to do this), and place the dough circles on the prepared sheet pan, leaving about 1 centimeter (about 1/2 inch) of space between the cookies.
Place the sheet pan in the fridge for approximately 10 minutes, so that the cookies can firm up.
Bake them for 10 to 12 minutes, or until they’re just starting to color around the edges. Lift the cookies onto a cooling rack and leave them to cool.
Once they’re at room temperature, top half of the cookies with dulce de leche, using about 1 teaspoon on each one. Then sandwich those cookies with the plain ones. As you press the cookies together, carefully rotate the two cookies in opposite directions, which will help spread the dulce de leche all the way to the edge of the cookies.
