In a large mixing bowl, cream the butter and granulated sugar until light and fluffy. Add the egg yolks and vanilla extract, mixing well. In another bowl, combine the all-purpose flour, cornstarch, baking powder, cocoa powder, and cinnamon. Gradually add the dry ingredients to the butter mixture until a dough forms.

Chill the Dough

Wrap the dough in plastic wrap and refrigerate for at least 1 hour until firm.

Roll and Cut

Preheat your oven to 350°F (175°C). On a lightly floured surface, roll out the dough to about 1/4 inch thickness. Use round cookie cutters to cut out cookies and place them on a baking sheet lined with parchment paper.

Bake

Bake for 10-12 minutes or until the edges are lightly golden. Allow cookies to cool completely on a wire rack.

Assemble with Dulce de Leche

Spread a generous layer of cinnamon dulce de leche between two cookies to form a sandwich. Dust the tops with powdered sugar.

Coat with Toasted Coconut

Roll the edges of the alfajores in toasted coconut flakes for extra flavor and texture.