Scald 1 cup of milk on the double boiler. Add the tapioca and cook for 20 minutes or until it is clear. Remove. Beat the egg yolk and add sugar and salt. Add the tapioca to the egg yolk mixture.
Put back over boiler and cook until thickened. Remove from heat. Add the stiffly beatened egg whites, vanilla, and chocolate and blend with the rest of the 1/2 cup of scalded milk.