Adjust oven rack to the middle position and heat oven to 350 degrees F. Lightly spray pan with nonstick cooking spray, line 8x8-inch baking pan with 2 pieces of foil, leaving a 3-inch overhang on all sides. Spray with nonstick cooking spray again, and set aside.
In a large heat-proof bowl add chopped chocolate and butter. Microwave on 50% power for 1 minute. Stir, and microwave on 50% power for 30 seconds. Stir, and repeat until chocolate and butter are melted and smooth. Whisk in cocoa powder until smooth. Set mixture aside to cool for 5 minutes.
Whisk eggs, sugar, vanilla, and salt into chocolate mixture until combined; then mix in flour with wooden spoon until combined. Finally, fold in chocolate chips.
Pour batter into prepared pan, smooth into corners, and level surface. Bake on middle rack until slightly puffed and a toothpick inserted in center comes out with just a few moist crumbs, about 35-40 minutes.
Cool brownies to room temperature on wire rack, about 2 hours. Remove brownies from pan using foil overhang, and cut into 12-16 squares. Serve naked or with your favorite frosting (I personally love these with a little peanut butter buttercream).