Alfajores de Maicenaare some of the tastiest alfajores; maicena--corn starch--is used along with flour to give the cookies a texture that is lighter than a typical shortbread cookie. That lightness still captures the cookie's buttery flavor, and together with dulce de leche, they will melt in your mouth. 
These cookies are great with coffee or tea, dipped in chocolate or covered in powdered sugar, but they are also nice just on their own. They will last for several days in a container with a tight-fitting lid. The dough may also be frozen for future use.
makes: 12 alfajores
2 sticks of butter at room temperature
 
1/2 cup sugar
 
1 egg plus one yolk
 
1 teaspoon vanilla
 
2 cups flour
 
1 cup cornstarch
 
1 teaspoon baking powder
 
1-2 cups dulce de leche (link to make your own, store-bought is also fine)
 
powdered sugar (optional)
 
In the bowl of a stand mixer, cream the butter and the sugar. Add in the egg plus yolk and vanilla and beat over medium speed until incorporated. In a separate bowl, mix the flour, cornstarch and baking powder together. Add the flour mixture to the butter mixture and continue mixing until it forms a consistent dough.
 
Remove the dough from the mixer and divide the dough into two balls. Wrap the balls in plastic wrap and refrigerate for at least half an hour or overnight.
 
Preheat the oven to 350 degrees Fahrenheit. Unwrap the dough and roll it out (it will be cold and stiff at first) onto a floured surface. Roll the dough out to about 1/4 inch thickness, then cut with a small round cutter (or a juice glass). Repeat the rolling and cutting until you have used all the dough. Place the cookies on a parchment-paper lined cookie sheet, and bake for 15 minutes, just until the edges start to brown.
 
Let the cookies cool completely, and then place a generous dollop of dulce de leche on one cookie, topping with another cookie to make a sandwich. Press gently together. Cover in sifted powdered sugar, if desired.