Preheat the oven to 200°C.
Melt the chopped chocolate and butter in a bowl over a pan of simmering water.
Remove from heat and stir in the vanilla extract, warm water, and sugar until smooth.
Whisk the beaten egg yolks into the chocolate mixture.
Fold in the sifted rice flour and baking powder ensuring no lumps remain.
Whisk egg whites in a clean bowl until stiff peaks form.
Fold whites gently into the mixture and pour into a greased dish.
Place dish into a bain-marie and bake at 200°C for 10 minutes.
Reduce heat to 160°C and bake for another 20 to 30 minutes until firm on top.
Dust with icing sugar and serve.