Cooking : Boston Cream Sponge Cake

Ingredients
1 cup sugar
1/2 teaspoon salt
1 teaspoon vanilla extract
1 1/4 cups all-purpose flour
3/4 cup sugar
2 tablespoons cornstarch
1 1/2 cups milk
6 egg yolks, beaten
1 teaspoon vanilla extract
1/2 cup butter (no substitutes), softened
CHOCOLATE FROSTING:
2 tablespoons butter, softened
1 (1 ounce) square unsweetened baking chocolate, melted and cooled
1 cup confectioners' sugar
3 tablespoons whipping cream
1 teaspoon vanilla extract

Directions
In a mixing bowl, beat eggs until light and fluffy. Gradually add sugar and salt, beating until thick and lemon-colored. Add vanilla; mix well. Fold in flour, 2 tablespoons at a time. Pour into two greased and floured 9-in. round baking pans. Bake at 350 degrees F for 17-20 minutes or until cake springs back when lightly touched. Cool for 10 minutes before removing from pans to wire racks to cool completely.
For custard, combine sugar and cornstarch in a saucepan. Gradually stir in milk until smooth. Bring to a boil; cook and stir for 2 minutes. Remove from the heat. Stir a small amount of hot mixture into egg yolks; return all to the pan. Bring to a gentle boil, stirring constantly. Remove from the heat; stir in vanilla. Cool completely. In a mixing bowl, cream butter. Gradually beat in custard.
To assemble, split each cake into two horizontal layers. Place bottom layer on a serving plate; top with a third of the filling. Repeat layers twice. Top with remaining cake layer. In a small mixing bowl, combine frosting ingredients. Spread over top of cake. Refrigerate.