Sift the cornstarch into a bowl to aerate it and remove any lumps—this ensures a smooth, tender cookie texture. Measure out all remaining ingredients and set them nearby. Place your oven rack in the middle position and preheat to 350°F so it reaches temperature while you prepare the dough.

In a medium bowl, combine the softened butter, sweetened condensed milk, vanilla extract, egg yolk, and salt. Mix with a wooden spoon or electric mixer until the mixture is pale, smooth, and well combined—about 1-2 minutes. The egg yolk acts as a binder while the condensed milk adds sweetness and moisture to create a tender crumb.

Gradually fold the sifted cornstarch from Step 1 into the wet ingredient mixture from Step 2, stirring gently until a smooth, cohesive dough forms. The dough will be slightly soft and delicate—avoid overworking it or the cookies will become tough. I find it helpful to use a spatula to fold rather than stir vigorously, which keeps the texture light and tender.

Using your hands, roll the dough into walnut-sized balls (about 1 inch in diameter) and place them 2 inches apart on parchment-lined baking sheets. Press each ball gently with your thumb to flatten slightly, then use the tines of a fork to create a crosshatch pattern—this is both decorative and helps the cookies bake evenly. Cover the sheets with plastic wrap and refrigerate for 30 minutes to set the dough and prevent spreading during baking.

Remove the chilled cookies from the refrigerator and place them in the preheated 350°F oven. Bake for 12-15 minutes, until the edges are light golden but the centers remain pale and soft—these cookies are meant to be tender and cake-like, not crispy. I like to check them at 12 minutes first, as oven temperatures vary, and they can overbake quickly.

Let the cookies cool on the baking sheet for 20 minutes—this allows them to set without becoming too fragile. Transfer them to a wire cooling rack to cool completely, about 1-2 hours, before serving or storing. The cookies will firm up as they cool to room temperature.