With an electric mixer beat the butter and sugar until light and fluffy.

Add in egg yolks and vanilla and beat until fully combined.

In a medium bowl, whisk together the flour, cornstarch, baking powder, baking soda, and salt, and then gradually add this mixture to the wet ingredients until fully incorporated, taking care not to overmix.

Form the dough into a flattened disc, wrap and refrigerate until chilled and firm, about 2 hours.

When ready to bake, preheat the oven to 350°F (180°C) and line two baking sheets with parchment paper.

On a floured surface, roll out the dough to a 1/8-inch (3mm) thickness, cut rounds using a 2-inch (5cm) cutter, and place on the prepared baking sheets. Reroll any scraps. Refrigerate the cut cookies for 15 minutes to keep them from overspreading, then

Bake for 7-10 minutes, or until the cookies are slightly golden brown at the edges. Let cool completely on wire racks, and then flip half of the cookies over.

Place the shredded coconut in a shallow bowl or plate. Set aside.

Spread about 1 teaspoon of dulce de leche on the flipped halves and then very gently sandwich with the top halves until the filling starts to ooze out. Roll the edges in the shredded coconut.

Store cookies in an airtight container at room temperature for up to 3 days