Mix sugar with melted butter and stir til combined.
Mix egg & vanilla and add it to the butter/sugar mix gradually.
Sift in the dry ingredients and mix til combined, don't over mix.
Pour into a lined oven dish of your choosing (Roughly same size as the box brownie)
Preheat oven to 180C and bake for 20-25 min
Remove & leave until it has cooled down completely (Preferably in the fridge a couple hours to go fudge like in the middle)
Notes
One of the very few recipes where a cocoa powder brownie recipe actually turns out nice. It will be more "raw cake batter" in the middle in you cut too early.