Method

Cut the unsalted butter into small cubes and tip into a medium sized bowl, then break the cooking dark chocolate into small pieces and add to the bowl.

Next, cover the bowl loosely with cling film and heat in the microwave for 2 minutes on high, until melted. 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 pre-heat the oven to 180°C/160°C (fan).

Using a shallow, 20cm square tin, cut out a square of non-stick greaseproof paper to line the base. Tip the plain flour and cocoa powder into a sieve held over a medium bowl. Tap and shake the sieve so flour and cocoa powder sift through together and any lumps are removed, then chop the 80% dark chocolate into chunks.

Into a large bowl, break the eggs, and tip in the golden caster sugar. With an electric mixer on maximum speed, whisk the eggs and sugar. Pour the melted chocolate mixture over the whipped eggs and gently fold together with a rubber spatula.

Hold the sieve over the bowl of chocolate mixture and resift the cocoa and flour mixture, shaking the sieve from side to side, to cover the top evenly.

Gently fold in the powder, using a figure of eight action. The mixture will look dry and dusty at first, but if you keep folding very gently and patiently, it will begin to look fudgy.

Finally, stir in the chopped 80% dark chocolate chunks until they’re dotted throughout.

Pour the mixture into the prepared tin, gently easing it into the corners of the tin and paddle the spatula from side to side across the top to level it, then place in the oven and cook for 25 minutes.

Remove from the oven and leave the brownies in the tin until completely cold. Once cooled, cut into quarters, then cut each quarter into four squares and serve.