Place the chopped chocolate in a heatproof bowl and melt gently over a double boiler or in short intervals in the microwave. Stir until completely smooth and set aside.

While the chocolate is melting, beat the eggs, light brown sugar and caster sugar until the mixture becomes pale, slightly thick and fluffy. Add the vanilla extract.

This step is important for creating the characteristic shiny, crackly brownie top.

Melt the butter in a saucepan over medium heat, stirring frequently. Continue cooking until it turns golden brown and smells nutty.

Remove from the heat and add the oil and cocoa powder. Stir well to combine.

Add the melted chocolate to the warm browned-butter mixture and stir until smooth and fully combined.

Slowly pour the warm chocolate mixture into the beaten eggs and sugar, mixing gently until everything is incorporated.

Sift the flour, cornstarch and salt over the batter. Fold gently with a spatula just until no dry streaks remain. Avoid overmixing to keep the brownies dense and fudgy.

Fold in the extra chocolate chunks, if using.

Line a 20 × 20 cm (8 × 8-inch) square pan with parchment paper and lightly grease it. Pour in the batter and spread evenly.

Bake in a preheated oven at 173°C / 350°F for 22–24 minutes.

Start checking around 18 minutes. The edges should be set, while the centre should still be slightly soft and a toothpick inserted in the centre should come out with moist crumbs.

Allow the brownies to cool before slicing. They will continue to set as they cool, giving you that perfect fudgy texture.