Break the chocolate into squares and put into a double boiler with the cream. Stand the double boiler over a pan of hot water and stir the chocolate until it is melted. Take it off the heat.
In another bowl beat the egg yolks and the sugar and gradually whisk the melted chocolate into them. If you dump hot melted chocolate straight into the eggs you have scrambled eggs and chocolate which doesn’t make many short lists for fab desserts anywhere. Place the chocolate/cream/yolk/sugar mixture in the double boiler over hot water and whisk for five minutes until the mixture is thick and creamy. Take it off the heat and add the rum. Stir to blend.
Beat the egg whites until they are really stiff and then fold them gently into the chocolate mixture. Turn the mousse into a glass bowl or into individual serving bowls and leave in the fridge for at least an hour before serving (I think it tastes better after 4-5 hours, and it will do well overnight). I think the mousse looks great in espresso cups – and they are just the right size. You don’t want to serve people too much mousse. It’s really rich and a few ounces will do. Just before serving decorate the mousse with whipped cream and a few chocolate shavings.
