In a large mixing bowl, mix all-purpose flour, cornstarch, baking powder, and salt and sift using a flour sifter.

Add cold butter, and cut into small pieces. Crush and rub the butter into the dry ingredients with your fingers until the sandy texture. Add sweetened condensed milk and mix until it forms a cookie dough ball. If the dough seems too dry, add 1 or 2 tablespoons of water.

Wrap the dough in plastic film and chill in the refrigerator for 30-45 minutes.

Preheat the oven to 390°F (200°C). Using a rolling pin, roll out the dough between two sheets of parchment paper to 3-4 mm thick.

Cut out the cookies using your favorite cookie cutter, for example, a round-fluted cutter. If the dough gets too soft to handle, place it back in the fridge for a few minutes.

Arrange the cutouts on a baking tray covered with parchment. Optionally, add a few flaked or slivered almonds to create a flower pattern. Then, just press them down slightly. For the second batch, re-roll the leftover dough, chill it if necessary, and cut cookies out until the cookie dough has been used.

Bake cookies in the preheated oven for 8 to 10 minutes, until the edges are lightly golden brown. Don't overbake your cookies: they tend to color quickly.

Remove cookies from the oven and let them cool down on the baking sheet for 5 to 10 minutes, then transfer them to a cooling rack. Dust with icing sugar.