In a large bowl, combine the flour, corn starch, baking soda, and baking powder. Set aside.
Cream together butter and sugar using an electric mixer. Mix in the vanilla bean paste, water, and lemon zest before beating in egg yolks one at a time.
Slowly stir the dry ingredients into your wet ingredients until completely combined. Do not overmix.
Form the dough into a ball and place it in the refrigerator to cool for at least 30 minutes.
After your dough has cooled, divide it in half. Roll it out on a lightly floured surface until it is approximately ¼” thick. Use a 1 ½” round cookie cutter to stamp out cookies and transfer them to a prepared baking sheet. Gather the scraps of dough and re-roll them, repeating the process until you have used all of the dough.
Place the trays of unbaked cookies in the refrigerator or freezer and preheat the oven to 350 degrees F.
Once the oven has preheated, transfer your cooled pans of cookies to the oven and bake for 8-12 minutes. The bottom of the cookie should be slightly golden, but the top of the cookie will still be pale.
Allow the cookies to cool on the pan for 2-3 minutes before transferring to a wire rack to cool completely.
Once the cookies have cooled, flip half of your cookies upside down and coat with a thick layer of dulce de leche. Top with the right-side-up cookies to create sandwiches. You may also roll the edges of the cookies in flaked coconut for a bonus pop of texture and flavor. Dust finished cookies with powdered sugar before serving.