275²µ/9¾´Ç³ú plain flour
1 tsp baking powder
½ tsp bicarbonate of soda
100g/3½oz light soft brown sugar
150²µ/5½´Ç³ú caster sugar
½ tsp fine sea salt
1 tsp vanilla bean paste
220²µ/7¾´Ç³ú white chocolate, roughly chopped
130g/4¾oz unsalted butter, softened
1 large free-range egg, plus 1 free-range egg yolk