Preheat your oven to 350 degrees. Make sure your 12 inch cast iron skillet is well greased.
In large mixing bowl, combine the butter and the white and brown sugars. Cream together until light and fluffy. Add in the eggs and vanilla. Beat until well combined.
In a separate mixing bowl, whisk together the flour, baking soda, and salt. Slowly add the dry ingredients to the wet ingredients, mixing on low. Fold in the chocolate chips and chopped peanut butter cups. Swirl in the caramel sauce- do not over mix the caramel into the cookie dough though.
Press the cookie dough into the prepared skillet. Bake for 25-30 minutes or until the edges are crisp and the cookie is golden brown.
Let cool to warm. Serve topped with a scoop of vanilla ice cream and a little more caramel sauce, if desired.