In a large bowl, whisk to combine the cornstarch, flour, salt, and baking powder, then set aside.

To the bowl of a stand mixer fitted with a paddle attachment (or a large bowl if using a hand mixer), add the softened butter, and sugar. Beat on medium speed for about 3 minutes or until light and fluffy.

Add the egg yolks and vanilla extract, then mix for 1 minute until combined. Scrape down the bottom and sides of the bowl with a rubber spatula and mix once more.

Add the flour mixture all at once. Mix on low speed for 30 seconds until just combined. Scrape the bowl down one last time and mix for a few seconds more.

Transfer the dough to a piece of plastic wrap and flatten it into one or two disks. Wrap well and chill for about 1 hour.

Preheat the oven to 350°F and bring the dough out onto the countertop to warm up for a few minutes.

Lightly flour the surface and the top of the dough. With a rolling pin, roll the dough to be ¼ to ⅛-inch thick. Use a 1¾ to 2-inch round cookie cutter to cut the dough into circles. Place the cookies on parchment or silicone-lined baking sheets. Re-roll any excess dough and cut or freeze for later.

Bake for about 10- 12 minutes, until the cookies are just set, and start to turn light brown on the edges, rotating the pans halfway through. Allow to cool on the baking sheet before assembling.

Once the cookies are cool, pipe or spread a dollop of dulce de leche onto the back of a cookie and sandwich it to the bottom of another cookie. Roll the edges of the cookie in shredded coconut and repeat the assembly for the remaining cookies.