Preheat oven to 375º Fahrenheit.
Lightly coat an 8-10 inch cast iron skillet with nonstick spray or butter.
In a large bowl, combine flour, baking soda and salt; set aside.
Melt 10 tablespoons butter in a medium saucepan over medium heat. Cook, whisking constantly, until the foam subsides and the butter begins to turn a golden brown, about 2 to 2-1/2 minutes. Be careful, the butter can burn very easily! Transfer butter to a heat proof bowl; allow to cool and set aside.
Using the same pan, stir in remaining 4 tablespoons butter until completely melted. In a seperate large bowl, combine both sugars, vanilla, brown butter and the 4 tablespoons of melted butter. Mix until well combined. Whisk in egg and egg yolk and stir. Add flour mixture, beating just until incorporated. Gently fold in chocolate chips.
Place mixture into the prepared skillet. Place into oven and bake until edges are golden brown, about 15 minutes. Carefully remove pan from oven, add additional chocolate, caramel/peanut butter and pretzels (if using) and place back in the oven for 3-5 minutes or until extra chocolate is melted.
Serve immediately, topped with ice cream, if desired. Enjoy!