Separate the eggs and beat the yolks with the sugar and powdered coffee until the mixture is thick and creamy. Melt the chocolate and water in a small saucepan; add the rum and stir into the egg and coffee mixture.

Whip the cream and fold it into the soufflé mixture. Whisk the egg whites and fold into the mixture. Pour into individual soufflé dishes or custard cups and freeze for 4 hours. Decorate with grated chocolate.