2 tbsp golden syrup
1 tsp bicarbonate of soda
75驳/2陆辞锄 caster sugar
flavourless oil (such as vegetable oil), for greasing
250g/9oz dark or milk chocolate, or a mixture
150驳/5陆辞锄 digestive biscuits
100g/3陆oz unsalted butter, cut into 1cm cubes