Preheat the oven to 350F and lightly coat a 10″ cast iron skillet with nonstick spray.

In a large bowl using a hand or stand mixer with the paddle attachment, add the butter, dark brown sugar, and granulated sugar. Mix on medium-high speed until light and fluffy (about 2-3 minutes).

Scrape down the bowl and add in the eggs. Mix again on medium-high speed for another 2-3 minutes, or until the mixture is pale and creamy.

Scrape down the bowl and mix in the vanilla extract.

In a separate bowl, whisk together the all purpose flour, cornstarch, baking soda, and salt.

Pour half of the dry ingredients into the wet ingredients and mix on low speed. Once almost combined, mix in the rest of the dry ingredients again on low speed.

Just before that’s combined, toss in the chocolate chips or chunks and use a rubber spatula to fold in by hand. Scoop the dough into the skillet and spread it even. Bake for 25 minutes, or until the edges are a pale golden brown (the cookie will darken as it cools). If you want a more well-done cookie, bake for an additional 5-8 minutes.