Break the chocolate into smallish even sized pieces. Place the chocolate into a heatproof bowl set over a saucepan of simmering water (make sure the water doesn't touch the bottom of the bowl). Allow the chocolate to melt over the heat.
Meanwhile, whisk together the icing sugar and double cream in a bowl until soft peaks form when the whisk is removed from the bowl. Lightly stir in the melted chocolate, creating a marbled effect. Divide the mousse mixture between two glass dishes and chill in the fridge for at least five minutes before serving.
To serve, remove the mousse from the fridge and top with the fresh raspberries.
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