90²µ/3¼´Ç³ú plain flour
150g/5½oz light brown sugar
300g/10½oz golden caster sugar
65²µ/2¼´Ç³ú cocoa powder
170²µ/5¾´Ç³ú dark chocolate (minimum 70% cocoa solids), roughly chopped
170²µ/5¾´Ç³ú unsalted butter, diced, plus extra for greasing
3 free-range eggs