In a small saucepan set over medium heat, add 8 tbsp. of butter. Heat until the butter foams then begins to brown and become speckled (about 3-5 minutes). Remove from the heat and pour into a medium size mixing bowl along with the remaining butter. Stir until all of the butter has melted. Add the sugars, egg, egg yolk and vanilla. Beat the mixture for 30 seconds, then let rest for 30 seconds. Repeat 3 times.
In a small mixing bowl whisk together the flour, salt and baking soda. Using a spatula or wooden spoon, stir in the dry ingredients. Fold in the chocolate chips and chocolate chunks, then press into a 10-12 inch cast iron skillet, creating an even layer.
Place in oven and bake until the center is set, about 20-25 minutes. Just remember with a cast iron skillet the cookie will continue to bake a little as it cools. Remove from the oven and allow to cool for 10-15 minutes before slicing and serving.
Notes
-I like to use either Ghirardelli or Scharffen Berger chocolate. They make quality chips, bars and chunks.