275驳/9戮辞锄 plain flour
1 tsp baking powder
陆 tsp bicarbonate of soda
100g/3陆oz light soft brown sugar
150驳/5陆辞锄 caster sugar
陆 tsp fine sea salt
1 tsp vanilla bean paste
220驳/7戮辞锄 white chocolate, roughly chopped
130g/4戮oz unsalted butter, softened
1 large free-range egg, plus 1 free-range egg yolk