Preheat the oven to 175C
Line a 23 x 23 cm square baking tray with baking paper
Place the chocolate, cocoa powder and butter into a heatproof bowl
Heat quarter cup of water in a saucepan on medium fire (Double boiler)
Place the bowl with chocolate and butter on top of the boiling water to melt the chocolate mixture
Once melted leave aside to cool down slightly
In a separate bowl whisk eggs, brown sugar, white sugar & vanilla (Use a stand mix or a handheld mixer)
Once its well whisked add in the melted chocolate and butter mix gradually while whisking
Lower the speed of the mixer fold in the flour and salt
Pour the batter to the cake tray and bake for 30 minutes
Take it out of the oven and let it cool completely before slicing