25g/1oz rice flour, sifted
1 tsp gluten-free baking powder
110g/4oz caster sugar
gluten-free icing sugar, for dusting
1 tsp pure vanilla extract
150g/5oz best-quality gluten-free dark chocolate (70 percent cocoa solids)
150g/5oz butter, plus extra for greasing
4 eggs, preferably free-range, separated