Preheat oven to 325 degrees.
Cream together sugars and butter with a mixer.
Add in eggs and vanilla and mix until combined.
Mix dry ingredients of flour, salt, baking soda together.
Add the dry ingredients to the wet ingredients and mix until a soft dough forms.
Fold in or mix in the chocolate chips.
Grease your cast iron skillet with butter.
Press your mixed dough into your cast iron about 1 inch thick and all the way to the edges. My 8 inch cast iron uses about 2/3-3-4 of the dough in the recipe.
Store any excess dough in the fridge and use within a few days, or put it in the freezer for longer keeping.
Baking time is very dependent on the thickness of your cookie cake and size of cast iron. Bake anywhere from 30-40 minutes or until the top begins to turn a light golden brown and does not look doughy.
Remove from the oven and let rest and cool. If you plan to put icing on your cake, wait until it has completely cooled first.
Enjoy!