To melt the chocolate
Melt the chocolate with the icing sugar and cream in a thin-sided bowl over a gently simmering bain-marie, stir until smooth. Remove the bowl, leave to cool.
To prepare the mousse
Beat the cream until stiff, fold in carefully using a rubber spatula. Spoon the mousse into glasses, cover and chill for approx. 2 hrs. Dust with cocoa powder.