Alfajores are tender sandwich cookie filled with a layer of dulce de leche and commonly rolled in coconut. The are popular cookie found in many Latin American countries and when packaged you can often find them dipped in chocolate. These are one of my families favorites!
In a mixing bowl, whisk together flour, cornstarch, baking powder and salt, set aside.
In the bowl of an electric stand mixer fitted with the paddle attachment, blend together butter and sugar on medium speed until creamy, about 30 seconds.
Blend in egg yolks one at a time. Mix in vanilla extract. With mixer set on low speed, slowly add in dry ingredients and mix until combined and dough starts to come together**.
Shape dough into a ball, cover ball with plastic wrap and refrigerate 30 minutes to 1 hour until dough is easy enough to work with.
Preheat oven to 350 degrees. Roll half the dough out onto a lightly floured surface to about 3/16-inch thickness.
Using a 2-inch round cookie cutter, cut dough into circles then using a thin metal spatula or tall knife (such as a Santoku knife), slide along the bottom of the cutout cookie and transfer cookie sheet lined with parchment paper or a silicone baking mat.
Bake in preheated oven for 10 - 11 minutes. Allow cookies to cool 5 minutes on cookie sheet then transfer to a wire rack.
Cool cookies completely then spread a layer of Dulce de Leche over the bottom side of one cookie, then sandwich to the bottom side of another cookie.
Roll in fine coconut if desired. Store cookies in an airtight container (I like to store them in the fridge).
Notes
For a light lemony flavor, you can also add 1 1/2 tsp lemon zest along with the butter and sugar mixture.*Spoon and level flour to measure and spoon and level or pour and level cornstarch to measure. For most accurate results just measure in grams.**Dough will seem dry and crumbly at first but keep mixing and it should come together well. If not you can mix in a teaspoon or two of milk to bind.