Preheat the oven to 350°F. In the bowl of a stand mixer or using a hand mixer, mix the flour, powdered sugar, and butter for 3-4 minutes. The mixture will resemble sand.

Whisk the egg, add it to the dough and mix until a dough forms, around 2 minutes. Divide the dough in half and place each half between two pieces of parchment paper. Roll out the dough to a thickness of ¼ inch.

Place the rolled dough in the freezer for at least 20 minutes, or until firm. Cut into circles using a 2.5” round cookie cutter and place on a cookie sheet lined with parchment paper or a silicone mat. If the dough has warmed up, place in the freezer for 15 minutes.

Bake for 20 minutes or until the cookies are golden. Cool on the baking sheet for 5 minutes and then transfer to a wire cooling rack to cool completely. Fill a piping bag with dulce de leche (if you don’t have one, you can use a Ziploc bag by cutting ½ inch from a corner).

Pipe the dulce de leche onto one cookie and place a second cookie on top to form a sandwich. Repeat with the remaining cookies. Roll the rim of each cookie in coconut flakes, then set aside. Using a sifter or fine colander, sprinkle powdered sugar on top of the cookies. Serve or store in an airtight container for up to one week.