Preheat oven to 325 degrees and place 1 cup of chocolate chips in a large mixing bowl. Place a 10" iron skillet (or any 10" oven-safe skillet with high sides) over medium heat and melt butter. Remove skillet from heat, pour hot butter over chocolate chips and allow it to sit for 1 minute to allow chocolate to melt.

Use a paper towel or pastry brush to lightly coat the inside of the skillet with residual butter from the pan and set aside. Stir butter and chocolate chips together with a whisk until combined and chocolate is melted. A few small lumps of chocolate may remain and that is okay, but the mixture should be relatively cool.

Add eggs, sugar, vanilla and salt to chocolate mixture and whisk until completely combined then sift flour, cocoa and baking soda on top. Fold dry ingredients into wet ingredients until no dry spots remain. Fold in nuts if desired.

Transfer batter into prepared skillet and bake 20–22 minutes or until top begins to crack, center is set and a toothpick comes out with a few moist crumbs attached. Remove from oven and sprinkle with additional ½ cup of chocolate chips and allow them to melt on the surface. Serve and enjoy!