In a small bowl add the flour and sift the cocoa powder and baking soda into the flour using a mesh strainer. Set aside.
Add the butter, brown sugar, and granulated sugar to a large bowl. Using a hand mixer, cream the sugar into the butter for about 2 minutes. Add the egg and vanilla extract and mix to combine.
Add the flour mixture into the butter-sugar mixture and mix at low speed. Otherwise, you will get flour and cocoa all over the place. Mix just until combined you don't want to over mix here.
Fold in the chocolate chips, caramel pieces, and chocolate chunks.
Preheat the oven to 350 degrees. Spray your cast iron pan with cooking spray. Spread the dough into the pan as evenly as you can. Top with the flaked sea salt and bake for 30-33 minutes or until desired doneness.