Alfajores

Preheat the oven to 350°F (180°C), or 160°C if using a fan oven. Line three baking sheets with parchment paper and set aside.
In a large mixing bowl, whisk together the flour, cornstarch, powdered sugar, baking powder and salt until combined; set aside.
In a separate large bowl, cream the butter and the granulated sugar until light and fluffy. Add the egg and egg yolk, along with the vanilla and beat well.
Add the flour mixture to the butter mixture in 2-3 smaller additions, mixing well after each.
Chill the dough at least 30 minutes, then use a rolling pin to roll it until it is ¼-inch thick. Use a 1.5-2-inch circular cookie cutter to cut the dough, then carefully transfer the circles to the prepared baking sheets at least 2inches apart.
Bake in the preheated oven for 8-10 minutes, or until the edges are lightly golden.
Allow the cookies to cool for 5 minutes before transferring to a cooling rack to cool completely.
Flip half of the cookies upside down so that the browned side is facing up, and pipe or spread a generous amount of dulce de leche on top. Place a second cookie, browned side down, on top of the dulce de leche and gently squish together.
Roll the exposed dulce de leche in shredded coconut if desired. Sprinkle cookies with powdered sugar before serving.