Preheat the oven to 350 degrees F (190 degrees C).
Whip butter with an electric mixer until fluffy. Stir in the confectioners' sugar, cornstarch, and flour. Beat on low for one minute, then on high for 3 to 4 minutes. Drop cookies by spoonfuls 2 inches apart on an ungreased cookie sheet.
Bake for 9 minutes in the preheated oven. Watch that the edges don't brown too much. Cool on wire racks.
