Preheat your oven to 350°F (175°C).
Cream together the softened butter and powdered sugar until light and fluffy.
Add the egg yolks and vanilla extract, mixing until well combined.
In a separate bowl, whisk together the flour, cornstarch, and baking powder.
Gradually add the dry ingredients to the wet mixture, stirring until a dough forms.
Roll out the dough to about 1/8 inch thick on a floured surface.
Cut out round shapes with a cookie cutter and place them on a lined baking sheet.
Bake in the preheated oven for 12-15 minutes, until lightly golden.
Allow the cookies to cool completely on a wire rack.
Spread a generous dollop of dulce de leche on one cookie and top with another.