Preheat the oven to 325 degrees F and grease a 10 or 12-inch cast iron skillet with vegetable oil and set aside.
In a large bowl or stand mixer fitted with a paddle attachment, cream together the butter and sugars until light and fluffy.
Beat in the eggs and egg yolk one at a time, mixing between each addition.
In a separate, medium bowl, whisk together the flour, baking soda, and salt.
Slowly add the flour mixture to the butter mixture with the mixer running on low speed just until combined.
Fold in the chocolate chips and chopped chocolate.
Press the cookie dough in the skillet and bake for 30 to 40 minutes.
Allow to cool completely before cutting and serving or scoop out while warm. Serve with ice cream, if desired.
Topping with flaky sea salt can make for a delicious flavor intensifier.
Salted or unsalted butter can be used on this recipe depending on how “buttery” of a flavor you want.
You can use either a 10 or 12-inch skillet for this recipe. The photos show a 10-inch which gives you a thicker edge where the 12-inch would be more even. The 12-inch skillet will require less baking time than the 10-inch.
Feel free to add in an additional ½ cup of mix-ins for a total of 2 cups. Add in options include M&Ms, toffee bits, etc.