Preheat oven to 350-degrees.
Mix the butter, sugar, brown sugar, eggs, and vanilla in a medium-sized bowl until well blended.
In a separate bowl mix the flour, baking soda, and salt.
Add the flour mixture to the sugar mixture and blend.
Add the chocolate chips and stir with a spatula.
Butter the cast iron skillet and add the entire cookie dough mixture. Press down with your hands until it is flattened.
Bake for approximately 30-40 minutes, or until cake tester comes out clean. (With my oven, I cooked the cookie for almost 40 minutes).