Sandwich Cookie with Dulce de Leche (Argentinean Alfajores Maicena)

These irresistible Alfajores are a soft, sweet and crumbly shortbread sandwich cookies filled with dulce de leche. A very popular recipe across Latin America but specially Argentina. There are a few different types of alfajores, this classic recipe uses cornstarch which is known as "Alfajores de maicena".

1 cup all-purpose flour, unbleached
1 cup cornstarch
1 tsp. baking powder
¼ tsp. baking soda
¼ tsp. sea salt
½ cup granulated sugar
8 Tbsp. (1 stick) butter, at room temperature
2 large egg yolks
2 tsp. lemon zest, finely grated, divided
1 tsp. pure vanilla extract
2 Tbsp. warm water
1 cup coconut flakes
1 can sweetened condensed milk

In a large bowl, sift together the flour, cornstarch, baking powder, baking soda and kosher salt. Set aside

In the bowl of an electric mixer, beat sugar and butter until light and fluffy, about 3 minutes. Add yolks and beat to combine. Add the vanilla extract, water and lemon zest beat until just combined. Add flour mixture, and mix on low speed until the dough just comes together. Wrap the dough in plastic and chill until firm, at least 2 hours.

Preheat an oven to 350°F (180°C/160°C fan, Gas Mark 4). Line baking sheets with parchment paper.

Remove dough from plastic wrap and place on a lightly floured surface, flour a rolling pin and roll out to about ¼" thick. Cut the dough with a 2" cookie cutter.

Place on prepared sheet pans, then bake until firm and edges are pale golden and the middle of the cookie is firm, about 9 minutes. Transfer baking pan to a rack and allow to cool completely before removing from baking sheet.

Spread 1 Tbsp. of dulce de leche onto the back of half the cookies. Place a second cookie on top and gently press to create a sandwich and repeat. Dust generously with powdered sugar before serving.

Roll sides in coconut and dust generously with powdered sugar before serving.