Preheat oven to 350F. Line two baking sheets with parchment paper. Beat butter until very light and fluffy. Add icing sugar and cornstarch and beat until well combined. Add vanilla, flour and and a pinch of salt. Mix well. Using a soup spoon, take equal size scoops of dough. Roll each scoop into a ball. Place on prepared pans and flatten with fingers. Bake for 20 mins. or until lightly golden. Remove from oven and place on a cooling rack.