Separate eggs and beat yolks with sugar and powdered coffee until mixture is thick and creamy. Melt chocolate and water in a small saucepan; add rum, and stir into egg and coffee mixture.
Whip cream and fold into soufflé mixture. Whisk egg whites and fold into mixture. Pour into individual soufflé dishes or custard cups and freeze for 4 hours. Decorate with grated chocolate.