185g unsalted butter
185g best dark chocolate
85g plain flour
40g cocoa powder
50g white chocolate
50g milk chocolate
3 large eggs
275g golden caster sugar
Melt 185g unsalted butter, cut into smallish cubes, and 185g best dark chocolate, broken into small pieces, in a double boiler. Leave the melted mixture to cool to room temperature.
While you wait for the chocolate to cool, position a shelf in the middle of your oven and turn the oven on to fan 160C/conventional 180C/gas 4 Using a shallow 20cm square tin, cut out a square of non-stick baking parchment to line the base.
Sieve together 85g plain flour and 40g cocoa powder over a medium bowl.
With a large sharp knife, chop 50g white chocolate and 50g milk chocolate into chunks on a board, so you end up with rough squares.
Break 3 large eggs into a large bowl and tip in 275g golden caster sugar. With an electric mixer on maximum speed, whisk the eggs and sugar until they look thick and creamy, like a milk shake. This can take 3-8 minutes, depending on how powerful your mixer is. You’ll know it’s ready when the mixture becomes really pale and about double its original volume.
Pour the cooled chocolate mixture over the eggy mousse, then gently fold together with a rubber spatula. The idea is to marry them without knocking out the air, so be as gentle and slow as you like.
Hold the sieve over the bowl of eggy chocolate mixture and resift the cocoa and flour mixture, shaking the sieve from side to side, to cover the top evenly. Gently fold in this powder using the same figure of eight action as before. The mixture will look dry and dusty at first, and a bit unpromising, but if you keep going very gently and patiently, it will end up looking gungy and fudgy. Stop just before you feel you should, as you don’t want to overdo this mixing. Finally, stir in the white and milk chocolate chunks until they’re dotted throughout. Now your mixing is done and the oven can take over.
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 in the oven and set your timer for 25 minutes. When the buzzer goes, open the oven, pull the shelf out a bit and gently shake the tin. If the brownie wobbles in the middle, it’s not quite done, so slide it back in and bake for another 5 minutes until the top has a shiny, papery crust and the sides are just beginning to come away from the tin. Take out of the oven.
Leave the whole thing in the tin until completely cold, then, if you’re using the brownie tin, lift up the protruding rim slightly and slide the uncut brownie out on its base. If you’re using a normal tin, lift out the brownie with the foil. Cut into quarters, then cut each quarter into four squares. They’ll keep in an airtight container for a good two weeks and in the freezer for up to a month.