250g/9oz plain flour
陆 tsp baking powder
陆 tsp bicarbonate of soda
110驳/3戮辞锄 light brown sugar
110驳/3戮辞锄 caster sugar
陆 tsp sea salt flakes, plus extra for sprinkling
陆 tsp vanilla extract
250g/9oz chocolate (see tip)
110驳/3戮辞锄 unsalted butter, diced and at room temperature
1 large free-range egg