This section is from the book "Queen's Of Cuisine", by Martha Logan. Also available from Amazon: Queens of Cuisine.
Filling and frosting for two 9-inch layers or three 8-inch layers.
1/4 cup Swift'ning 1/2 teaspoon vanilla.
1/4 cup boiling water 1/2 cup sifted cocoa.
1/2 teaspoon salt 1 1/2 cups sifted confectioner's.
1 egg yolk sugar.
Put Swift'ning into bowl. Add water and stir to blend. Beat in salt, egg yolk, vanilla and cocoa sifted with sugar. Beat well. Spread on cake cooled to room temperature (70° F.).