250g/9oz plain flour, sifted
2 tsp baking powder, sifted
375g/13oz caster sugar
100驳/3陆辞锄 cocoa powder
225g/8oz icing sugar, sifted
1 tsp vanilla bean paste
200g/7oz good-quality white chocolate, broken into pieces
300驳/10陆辞锄 butter, plus extra for greasing
125驳/4陆辞锄 butter, at room temperature
3 large free-range eggs
150ml/录 pint soured cream
150ml/录 pint Irish stout
75ml/5 tbsp Irish cream liqueur