Step 1: Place the chocolate in a heatproof bowl over a pan of gently simmering water (don't let the bowl touch the water). Stir until melted. Remove bowl from heat and set aside to cool slightly.
Step 2: Place eggs and sugar in a large bowl and beat with electric beaters for 5 minutes, or until mixture is pale, thick and doubled in volume. Fold in cooled chocolate and cocoa powder until combined.
Step 3: In a separate bowl, whip cream until thickened (be careful not to over-beat). Use a large metal spoon to carefully fold the cream into the chocolate mixture, trying to keep the mixture as light as possible. Spoon into 6 serving glasses and chill in fridge for at least 1 hour. Remove from fridge 15 minutes before serving, then top with extra whipped cream and grated chocolate to serve.
See more at:
http://www.taste.com.au/recipes/4857/chocolate+mousse+in+minutes