Preheat oven to 350 degrees. Line a 9X13 baking dish with foil and spray with a non stick cooking spray. I like to use Pam. Combine cocoa and melted butter in bowl and mix with an electric mixer. Then add flour and sugar and continue to beat together. Next add eggs and vanilla. Mix until combined, but don't over mix. The batter will be thick.
Next spread into prepared baking dish and spread evenly. The batter will be thick, so this may take a moment. Bake for 25-30 minutes or until fork inserted in center comes out clean. It took mine exactly 30 minutes, but all ovens vary.
Let cool 15 minutes and add frosting. You will want the brownies warm when you add the frosting.