2 tbsp golden syrup
1 tsp bicarbonate of soda
75²µ/2Β½΄Η³ϊ caster sugar
flavourless oil (such as vegetable oil), for greasing
250g/9oz dark or milk chocolate, or a mixture
150²µ/5Β½΄Η³ϊ digestive biscuits
100g/3Β½oz unsalted butter, cut into 1cm cubes