In a large bowl, stir together the condensed milk and butter until combined.
Slowly stir in the cornstarch to the condensed milk and butter mixture. When a dough begins to form use your hands to knead in the remaining cornstarch until it forms a smooth dough. You might not use all of the cornstarch.
Measure 1½ tsp. of dough and roll into a ball. Place onto a parchment lined baking sheet spaced 1" apart.
Create a striped pattern by pressing the tines of a fork into the dough balls.
Bake for 13-15 minutes or until the edges of cookies barely turn golden. The cookies should remain pale.
Allow the cookies to cool for 10-15 minutes before transferring to a rack to finish cooling. Serve with a cup of coffee or hot chocolate.