Lightly grease a 10 inch / 25 cm cast iron skillet.
In a medium bowl whisk together flour, baking soda and salt.
In a large bowl beat butter until creamy, then add the sugars, eggs and vanilla and beat to combine.
Add the flour mixture to the creamed mixture and mix with a spatula, wooden spoon or if using a stand mixer then mix on low speed with the flat beaters, then mix in the chocolate chips. Combine into a firm dough and wrap with plastic, refrigerate for 15 - 20 minutes.
While dough is in the fridge, pre-heat oven to 350F/180C.
Remove from the fridge and place half the mixture on the bottom the skillet (10 inch skillet), top with the melted chocolate and cover with the remaining cookie dough.
Bake for approximately 20 minutes. Let cool or eat warm, top with vanilla ice cream if desired. Enjoy!
Notes
The dough can be prepared in advance and refrigerated for up to 48 hours; let it sit at room temperature for 30 minutes before baking.
While a cast-iron skillet provides even heat distribution and a crisp edge, you can use any oven-safe skillet; just be aware that cooking times may vary.Any leftovers should be stored in an airtight container and refrigerated. It will keep for up to three days in the fridge. It can also be frozen in a freezer container, it will keep for up to three months in the freezer.