Preheat oven to 350° Fahrenheit and line two cookie sheets with parchment paper. Set aside.
Add the all-purpose flour, cornstarch, salt, baking powder, and baking soda to a medium size bowl. Stir briefly to combine and set aside.
In a bowl of an electric mixer fitted with a paddle attachment over medium/high speed, cream the butter and sugars until light, about 3-4 minutes.
Add the eggs and yolk one at a time, incorporating the eggs into the butter/sugar mixture before each addition. Add the vanilla extract and beat until combined. Stop and scrape the mixer to incorporate ingredients.
Turn the mixer speed to low and add the flour all at once. Mix until moistened. It's cool if you see bits of flour. Remove bowl from mixer and fold in the chocolate chips. Be sure to fold from the bottom to incorporate the ingredients. Cover the dough with plastic wrap. Place in the refrigerator for at least an hour.
Remove bowl from fridge. With a cookie scoop, scoop balls of cookie dough on the parchment lined cookie sheet about 2 inches apart.
Place in the oven and bake for 10-12 minutes (I usually bake for 10). Cookies will appear slightly under baked and that's cool. Remove from the oven and allow to cool in the cookie sheet for about 5 minutes, then transfer to a wire rack to cool completely.
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