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.

Preheat oven to 350 degrees F. Prepare baking sheet and spray with cooking spray or parchment paper. Using a cookie scoop, scoop about 1 1/2 inch to 2 inch cookie dough. Roll dough into ball, place on sheet and lightly press (if desired). Bake for 8-9 minutes, removed from oven and while still hot, slightly press down. Add chocolate chips to the top by lightly pressing chip in, if desired. Allow cookies to cool down before transferring. Cookies will slightly harden within a few hours or overnight.