Scald one and three-fourths cups milk, add corn-starch diluted with remaining milk, and cook eight minutes in double boiler; melt chocolate over hot water, add four tablespoons sugar and hot water, stir until smooth, then add to cooked mixture; beat whites of eggs until stiff, add gradually powdered sugar and continue beating, then add unbeaten yolks, and stir into cooked mixture; cook one minute, add vanilla, and cool before serving.