Put a small basin over a pan of barely simmering water. Add the coffee granules to it. Add 2 tsp hot water and stir to dissolve the granules. Break the chocolate into small pieces and add it to the basin. Stir until you have a smooth sauce. Remove the mixture from the heat, beat the egg yolk and add it to the mix. Stir in the rum, and leave it to cool for about 10 minutes.
In a large bowl, whisk up the egg white until it forms soft peaks. Using a metal spoon, fold the chocolate mixture into the egg whites. Spoon the whole lot into a glass, cover and refrigerate for a couple of hours.
To serve, mix together the dissolved coffee granules and the cream, and pour them over the mousse. Sprinkle with a little grated chocolate.
From the Dinner Co-op