150²µ/5¼´Ç³ú plain flour
1 tsp bicarbonate of soda
75g/2½oz light brown sugar
50g/2oz caster sugar
30g/1oz cocoa, sifted
½ tsp salt
1 tsp vanilla extract
125g/4oz dark chocolate
350²µ/12¼´Ç³ú dark chocolate chips
125g/4oz unsalted butter, softened
1 free-range egg, cold from the fridge