Preheat oven to 350 degrees F and prepare a 9x13 baking dish with butter or nonstick baking spray. You can also line it with parchment paper for easy cleanup.
Combine the flour, cornstarch, baking soda, and baking powder in a bowl and set aside.
In a large bowl, combine the melted and cooled butter, granulated sugar, and brown sugar and mix until well combined.
Add in the eggs and vanilla and mix until well combined.
Add the flour mixture in slowly, mixing in between, until all of the flour is mixed in.
Fold in the chocolate chips.
Using a spatula, spread the cookie dough into your prepared pan.
Sprinkle the top with extra chocolate chips if you would like them to look like ours on top.
Bake the cookies for 25-27 minutes, rotating once in between if needed for your oven. Cook 2 minutes more for a crispy cookie bar.