***Cake*** 10 ounces semisweet chocolate, finely chopped 1 1/4 cup butter, softened 1 1/2 cup sugar 8 eggs, separated 2 teaspoons vanilla extract 6 ounces roasted unsalted peanuts, chopped 1 cup cake flour 1 pinch cream of tartar 5 egg yolks ***Frosting*** 1 1/2 cup sugarPLUS"PLUS" means this ingredient in addition to the one on the next line, often with divided uses 1 1/2 tablespoon sugar 1 1/2 cup water 10 ounces butter, softened 10 ounces chocolate coated nougat or caramel candy bars, chopped
Preheat oven to 350 F Grease three 8" round cake pans. Line bottoms with wax paper.
Melt chocolate in top of double boiler over simmering water; stir until smooth. Cool.
Cream butter until light and fluffy. Gradually add 1&1/4 cups sugar, beating until smooth. Beat in egg yolks 1 at a time. Mix in vanilla. Stir in chocolate, then peanuts. Sift flour over batter and fold in. Beat egg whites with cream of tartar to soft peaks. Gradually add remaining 1/4 cup sugar and beat until still but not dry. fold 1/2 of whites into batter, then fold in remaining whites.
Divide batter among prepared pans. Bake until tester inserted in center comes out clean, 25 to 30 minutes. Cool 10 minutes, turn out onto racks and peel off paper. Cool to room temperature.
Beat yolks in bowl until pale yellow and ribbons from when beater are lifted, about 5 minutes.
Stir sugar and water in heavy saucepan over low heat until sugar dissolves.
Increase heat and boil without stirring until candy thermometer registers 234 to 240 deg f. (soft ball stage). Beat hot syrup into egg yolks in slow steady stream. Continue beating until thick and cool. 10 minutes.
Melt chocolate in top of double boiler over simmering water, stir until smooth. Remove from water and let stand until cool but still liquid.
Gradually beat butter into yolk mixture 1 tablespoon at a time. Add chocolate and stir to combine. Transfer 2 cups buttercream to small bowl, stir in candy bars.
Place one cake layer on platter top side down. Spread half of the candy bar buttercream over. Top with second layer. Spread remaining buttercream over. Top with third layer. Spoon 1 cup plain buttercream into pastry bag fitted with medium star tip. Frost tip and sides of cake with remaining buttercream.