Preheat the oven to 180ºc/160ºc fan and line a deep 9" square tin with parchment paper
Add the dark chocolate and butter to a bowl and melt together until smooth. Leave this to cool for 10 minutes.
Add the eggs and sugar to a new bowl, and whisk together for a few minutes until thickened, doubled in volume and the whisk leaves a trail in the mixture when you lift it out
Fold through the melted chocolate and butter carefully, and then fold through the plain flour and cocoa powder as well.
If you are using chocolate chips, fold them through now.
Pour the mixture into the prepared tin, and bake for 25-28 minutes in the oven - look for a small wobble in the middle of the mixture to know that they are ready.
Leave the brownies to cool for an hour.
Cookie Dough
To treat your flour - sprinkle it onto a baking tray, and bake in the oven for 5 minutes. Let it cool before using.
Add the unsalted butter and light brown soft sugar to a bowl and mix together
Add the flour, vanilla, milk and chocolate chips and mix together
Spread and press this over the cooled brownies
Ganache
Add the dark chocolate, milk chocolate and double cream to a bowl and heat in short bursts until the mixture has melted and combined.
Spread the ganache over the cookie dough and then set the cookie dough brownies in the fridge for several hours (but overnight is best!).
Portion, and enjoy!
Notes
These brownies will last for 3-4+ days, preferably in the fridge