Preheat the oven to 350F and line two baking trays with parchment paper,or lightly grease.
Cream the butter, brown sugar, and sugar togheter until fluffy.Beat in the the egg and then vanilla.
In a separate bowl, stir the flour, cornstarch, baking soda and salt. Add the flour mixture into the butter mixture until evenly blended.Stir in the chocolate chips.
Drop the dough by tablespoons full onto the prepared baking trays, leaving 1 1/2 inches between cookies.
Bake for about 10 minutes until the cookies are golden brown.Let the cookies cool on the tray for 5 minutes, then transfer the cookies to a rack to cool completely. The cookies can be stored in an airtight container for up to 3 days.
Makes about 2 1/2 dozen cookies.