Turn the oven on to fan 160C/conventional 180C/gas 4

Cut all of the butter into small cubes and tip into a small bowl. Break all of the dark chocolate into small pieces and drop into the same bowl.

Fill a small saucepan with enough hot water that when the small bowl of butter and chocolate sits on top and rests on the rim of the pan it doesn't touch the water. Put the pan over a low heat until the butter and chocolate have melted, stirring occasionally to mix them. Remove the bowl from the pan and allow to cool to room temperature.

Line the base of a 20cm square tin with a square of non-stick baking paper while you're waiting for the mixture to cool.

Tip the plain flour and cocoa powder into a sieve held over a new bowl. Tap and shake the sieve so they run through together and you get rid of any lumps.

Break all of the white and milk chocolate into small pieces and put to one side.

Break the large eggs into another large bowl and tip in the caster sugar. Whisk these together until the mixture looks thick and creamy, almost like a milkshake.

Pour the cooled chocolate mixture over the eggy milkshake mixture and gently fold them together with a rubber spatula being careful to not knock out the air. As they come together you'll see it go a dark mottled brown.

Gently fold in the flour and cocoa powder. Be patient and keep going - it will soon start to look and feel a bit fudgy.

Stir in the white and milk chocolate bits making sure they're distributed evenly throughout the mixture.

Pour the mixture into the prepared tin, scraping every bit out of the bowl with the spatula. Gently ease the mixture into the corners of the tin and paddle the spatula from side to side across the top to level it.

Put it in the oven and bake for 25 minutes. After that time take a look and gently shake the tin. If the brownie wobbles in the middle then it's not quite done so put it back in for another 5 minutes.

Take it out of the oven and leave to cool. Cut into decent sized squares and serve warm with a little ice cream or cold with some cream and raspberries...