Combine butter and cream cheese in a bowl fit with with paddle attachment of mixer. Cream together for about 1 minute. Add brown sugar and granulated sugar and continue to mix. Add egg and vanilla extract and continue to beat on medium to high speed until light and fluffy, about 5-7 minutes. Add half the flour, baking soda, salt, cornstarch and the rest of the flour. Mix to combine, 1 minute. Stir in chocolate chips until well combined. Cover and refrigerate dough at least 2-3 hours or up to a few days.