In a stand mixer, combine the butter and powdered sugar using the flat beater attachment. Add the cornstarch, flour, and baking soda, mixing until you achieve a crumbly texture as demonstrated in the video. Incorporate the egg yolks and blend until the dough forms (avoid overmixing after adding the yolks to maintain crispiness). Divide the dough into two pieces and refrigerate for 30 minutes.

Preheat the oven to 330°F (165°C).

Roll out the dough to a thickness of ¼” (½ cm) and cut out circles using a cookie cutter or glass. Bake for 10 minutes.

Allow the cookies to cool for about 5 minutes.

Spread the milk jam on one cookie, top with another cookie, and roll it in coconut flakes. Repeat this process until all cookies are complete.