In a large mixing bowl, beat together the softened butter and confectioners' sugar for 3-4 minutes until light and fluffy. If desired, add your choice of vanilla, lemon, or orange extract and mix briefly.
Gradually add the sifted flour and cornstarch to the mixture, beating only until the ingredients are just combined.
Shape the dough into 36 evenly sized balls. Arrange these on a baking tray lined with parchment paper or a lightly floured large plate. Gently press each cookie ball with a fork dipped in cornstarch or flour and top with sprinkles if desired.
Chill the dough balls in the refrigerator for approximately 2 hours or until firm. To expedite, freeze the dough balls until they become firm.
Preheat the oven to 300°F (150°C) while the cookies chill. When ready, bake cookies for 19-20 minutes or until the tops are set.
Allow cookies to cool on the baking tray before serving or storing.