Preheat the oven to 350°F and line a large jelly roll pan4 with parchment paper and spray with nonstick cooking spray. Set aside.
In a medium bowl, whisk together the flour, cornstarch, baking soda, and salt. Set aside.
In a large bowl with a hand mixer or a stand mixer fitted with a paddle attachment, cream together the butter, sugars, and vanilla until pale.
Add the eggs one at a time mixing just until combined. Scrape down the sides of the bowl as needed.
Add the flour mixture to the butter mixture and mix just until combined.
Mix in the chocolate chips.
Spread the cookie dough out on the parchment-lined jelly roll pan and use your hands or a rubber spatula to spread the dough all the way to the edges. It might seem like there isn't enough dough, but trust me, there is.
Bake for 17 to 20 minutes. The edges should be a nice golden brown, the cookies should look a little ripply, and the center will still be soft. Allow the cookies to cool for 20 to 30 minutes in the pan before using a pizza cutter to slice them into squares.5