Simmer the barley in the water in a covered saucepan for 45 minutes or until all the water is absorbed.
Chill.
Into another saucepan measure the butter or margarine and chocolate, and melt together over low heat.
Stir occasionally.
Blend the 2 tablespoons sugar and the cornstarch, and add milk and egg yolks.
Beat until the egg yolks are thoroughly mixed.
Add to the melted chocolate, turn up heat, and cook and stir until the mixture thickens.
Remove from heat.
Add barley, 1 teaspoon vanilla, and nuts.
Cool to room temperature.
Whip egg whites until they peak.
Add 4 tablespoons sugar, and whip again until stiff.
Fold into the barley mixture, and refrigerate.
When ready to serve, add the remaining 1 teaspoon vanilla and 2 tablespoons sugar to the whipped cream.
Layer in parfait glasses, beginning with the barley mixture.
Top with a dollop of whipped cream and a maraschino cherry.