Preheat the oven to 350F. Grease a skillet pan with butter. We used a 9 inch skillet.
Put the flour, baking soda, salt and cornstarch into a small bowl and mix it together. Set aside.
In a large mixing bowl add the melted butter, white sugar and brown sugar and beat with a handheld electric mixer until creamy (about 2 minutes).
Add the egg and vanilla extract and beat well to combine.
Tip the dry ingredients into the wet ingredients and mix until a thick dough forms.
Add most of the chopped chocolate reserving a small handful for later and mix until the chocolate is evenly dispersed through the dough.
Add half of the cookie dough to the skillet. Use your hands to press it down.
Spread 3/4 of the caramel sauce on top of the cookie dough.
Add the remaining cookie dough on top of the caramel sauce. The easiest way to do this is to use your hands to pat it into roughly the same size as the skillet then use your fingers to spread it to the edges.
Bake in the center of the preheated oven for 20-25 minutes or until the edges of the cookie are golden brown.
Remove from the oven and add the chocolate you reserved earlier.
Serve warm with ice cream and the remaining caramel sauce.
Notes
Instead of chocolate chips we used a bitter-sweet chocolate bar and roughly chopped it. This left large pockets of melted chocolate throughout. You can use chocolate chips if you prefer.
The salted caramel sauce we used was store-bought but you can absolutely make and use your own. If you are not a fan of salted caramel, this recipe works just as well with regular store-bought or homemade caramel sauce.
This recipe was baked in a 9 inch cast iron skillet, however, the ingredient quantities will work for an 8 inch or 10 inch skillet as well. Your cookie will be thicker or thinner depending on the size of your skillet. If you don’t have a cast iron skillet this recipe can be baked in a cake pan instead.