In a bowl, sift together the flour, cornstarch, and baking powder.

In another bowl, beat the butter, sugar, vanilla extract, and egg.

Add the flour mixture to the butter mixture and mix well. Chill the dough in the refrigerator for 15 minutes.

Lightly flour your work surface. Roll out the dough to 1/4 inch (about 0.5 cm) thick and use a round 3-inch (8 cm) cookie cutter to cut circles until all the dough is used.

Preheat the oven to 350°F (175°C). Place the dough circles on a baking sheet lined with parchment paper and bake for about 16 minutes.

Let the cookies cool. Spread dulce de leche on half of the cookies, then top with the remaining cookies, pressing gently. Spread more dulce de leche around the edges and roll the sides in shredded coconut.

You can toast the coconut before adding it to the alfajores. I think it tastes even better that way.