115g/4oz plain flour
150驳/5陆辞锄 light brown sugar
150驳/5陆辞锄 caster sugar
2 tbsp cocoa powder
陆 tsp fine sea salt
1 tsp vanilla bean paste
175g/6oz dark chocolate, broken into small pieces
150驳/5陆辞锄 shortbread biscuits, roughly chopped (optional)
175g/6oz unsalted butter, plus extra for greasing
3 large free-range eggs