- 1¼ cups all-purpose flour
- 3/4 cup cornstarch
- 1 teaspoon baking powder
- ¼ teaspoon salt
- 8 tablespoons (1 stick) unsalted butter, at room temperature
- ½ cup granulated sugar
- 1 large egg plus 1 egg yolk, beaten together
- 2/3 cup store-bought dulce de leche (see Note)
- Confectioners' sugar for garnish (optional)
2. Divide the dough in half and shape each portion into a thick disk. Wrap each in plastic wrap or wax paper. Refrigerate until chilled and firm enough to roll out, at least 2 hours and up to 1 day. (If the dough is very chilled and hard, let it stand at room temperature for 10 minutes before rolling out.)
3. Position a rack in the center of the oven and preheat the oven to 350F. Line two large baking sheets with parchment paper.
4. Unwrap one portion of dough and place on a lightly floured work surface. Dust the top with flour and roll out 1/8 inch thick. Using a 2¼-inch-wide heart-shaped cookie cutter, cut out hearts of dough and transfer them to a baking sheet, placing 1 inch apart. Gather up the scraps and roll out until all of the dough has been cut out. Repeat with the other portion of dough.
5. Bake until cookies look set and dry, but are not browned at all, 12 to 14 minutes.
6. Let cool on the baking sheets for 5 minutes. Transfer to wire cake racks and let cool completely.
7. For each cookie, dollop about 1 teaspoon of the dulce de leche onto the flat side of a cookie, then top with a second cookie, flat sides facing. Press gently to make the two cookies adhere. (The cookies can be stored in an airtight container for up to 4 days.) Just before serving, sift confectioners' sugar, if using, over the tops of the cookies.
Note: Dulce de leche can be purchased in cans or jars at Latino groceries and many supermarkets and specialty food stores. You can buy authentic Argentinean dulce de leche online from www.amigofoods.com. Leftover dulce de leche can be refrigerated in a covered container for up to 2 weeks. It is great stirred into hot tea instead of milk and sugar.