In a medium bowl, stir together the flour, cornstarch, and confectioners' sugar. Cut in the margarine; mix until a dough forms. Roll dough into 1 inch balls and place them on an unprepared cookie sheet. Flatten each ball slightly, using the back of a fork to make a criss cross pattern.
Bake for 20 minutes in the preheated oven, edges will be slightly browned.
