Preheat oven to 300°F. Lightly grease a baking sheet.
In a large bowl, whip butter until light and fluffy (about 5 minutes). Gradually blend in sugar and whip another 5 minutes. Add cornstarch and flour gradually and beat an additional 2 minutes.
Turn dough out onto counter. Work and knead dough until a soft, smooth ball is formed.
Pinch off pieces of dough and form into 1" wide balls. Place 1 1/2" apart on prepared baking sheet. Flatten with a floured fork.