Preheat the oven to 350-degrees F. Spray 9 by 13-inch pan with non-stick spray and place 1 piece of parchment paper to line the bottom of the pan.
Cream the butter and sugar in a mixer. Scrape down both sides. Then add the eggs 1 by 1. Add the salt and flour and mix until smooth. Remove the bowl from mixer and pour in cooled melted chocolate, mix well with a spatula. Add chopped chocolate last, fold quickly, then put in the prepared pan. Level out batter in pan. Place in preheated oven and bake for 45 minutes to 1 hour or until skewer comes out clean. Cool completely before cutting.