Alfajores - Dulce de Leche filled Sandwich Cookies have a tender, crisp and delicate texture. They're filled with creamy dulce de leche. Easy to make, impressive, and delicious!
In a large bowl, whisk or sift together cornstarch, flour, baking powder, and salt. Set aside.
In a mixer fitted with the paddle attachment, beat butter and sugar over medium speed until fluffy. Add brandy, cognac, or rum (optional) and lemon zest. Continue mixing. Add egg yolks one at a time and mix until combined. Decrease mixer speed to low and add dry ingredients. Mix just until no flour is visible.
Remove dough from bowl and knead for a few seconds in your hands. Divide dough in half and shape into two balls.
To roll out, place one of the dough balls on a large, rectangular piece of plastic wrap. Flatten slightly into a rectangular shape. Cover with a piece of wax paper. Using a rolling pin, roll into 1/8-1/4 inch thickness. Refrigerate dough for 20 minutes. Repeat with second dough ball. Re-roll any scraps and repeat.
Heat oven to 350 degrees and line a cookie sheet with parchment paper.
Remove dough from refrigerator. Using a 2 inch cookie cutter, cut out cookies and place on prepared cookie sheet.
Bake for 10-12 minutes or until cookie edges are slightly golden. If your cookie sheet is dark in color, cookies will be done sooner.
Cool cookies on cookie sheet for 5 minutes. Then, place them on wire rack and cool to room temperature.
Flip half of the cookies over and top each half with dulce de leche using a butter knife or a piping bag. Top with remaining cookies.
Place powdered sugar into a fine mesh strainer and sprinkle powdered sugar over cookies.
These cookies are best the same day they're made as they lose a little crispness as they sit.
Store at room temperature.