To begin, preheat your oven to 350 and line two pans with parchment paper.
In a large mixing bowl, add your butter and sugars and cream them together with a hand mixer for a couple minutes. Add in your egg and vanilla and lightly blend it together again.
In a separate mixing bowl, add your dry ingredients and stir them together (flour, cornstarch, baking soda and salt).
Pour your dry ingredients into your wet ingredients and stir/fold them together till you have one consistent, thick cookie dough. Add your chocolate chips and fold them into your batter.
Scoop your cookie dough onto your pans with a small cookie scoop, evenly spaced apart (at most 12 cookies per pan).
Bake for 10-12 minutes, or till the edges of the cookies are just set and the center is still a touch underdone.
Let the cookies cool for about 20-30 minutes on the pan, and then transfer them to a cooling rack till they are cooled entirely.
Stored in an airtight container, these cookies taste best within the first 4 days. You can also freeze them (after baking) if you'd like to eat one a couple months later!