1. Preheat oven to 300°F (150°C). Mix butter, sugar and vanilla thoroughly using an electric mixer. Gradually blend in flour and corn starch.

2. Form into 1-inch (3cm) balls and place on ungreased baking sheets. Gently press down on each cookie to flatten using fingers or a flat-bottomed drinking glass (dipped in sugar to prevent sticking).

3. Bake at 300ºF (150°C) for 25 to 30 minutes, or until bottoms begin to brown. Cool for 5 minutes; remove to a wire rack to cool completely.

4. RECIPE NOTE: For European-style shortbread, turn dough onto a lightly floured surface and knead until smooth, about 2 minutes. Pat into a 1/3-inch (1cm) thick rectangle measuring 11 x 8-inch (28 x 20cm). Cut into 2 x 1-inch (5 x 3cm) strips. Place 1-inch (3cm) apart on ungreased baking sheets. Prick with a fork. Bake as above.