Chocolate Banana Cream

Combine gelatine, cocoa and of sugar in the top of a double boiler. Beat together the egg yolks and milk and add to cocoa mixture. Cook over hot water stirring constantly until gelatine has dissolved and the mixture has thickened. Remove from heat, add vanilla and chill until mixture is just beginning to set. Beat egg whites until stiff, then lightly beat in the castor sugar. Fold in the cocoa mixture and mashed banana. Turn into serving dish and chill until firm.