Preheat oven to 350F then line a 9x13in. baking dish with foil and spray with non-stick spray. Set aside. Add melted butter and cocoa powder to a stand mixer and blend until smooth with the paddle attachment. Add in flour and sugar and beat together. Add eggs and vanilla and mix until just combined. Pour batter into prepared baking dish and smooth. Bake for 25-30 minutes. Let stand 15 minutes before frosting. Spread frosting over warm brownies and let cool completely before cutting and serving
Beat together all the frosting ingredients until smooth.