1-1/2 c. butter, softened
4 large eggs
1-2/3 c. all purpose flour
1-1/2 c. buttermilk
1-1/4 t. baking soda
2-1/2 8-oz. packages semisweet chocolate squares (20 squares)
Grease a 10″-x-2-1/2″ springform pan; line bottom of pan with waxed paper; grease waxed paper.
Separate 2 of the eggs. Put the yolks in small bowl and set aside. Also put the whites in another small bowl, cover bowl with plastic wrap; refrigerate to use for frosting later.
In large bowl, with mixer at low speed, beat 1-1/3 c. sugar, 1/2 c. butter, and 1-1/2 t. vanilla until blended. Increase speed to high; beat until light and fluffy.
Reduce speed to low, add the yolks and 2 whole eggs. Gradually add flour, buttermilk, baking soda, 2/3 c. cocoa, and 1/2 t. salt beat until blended, constantly scraping bowl with spatula. Increase speed to medium; beat 2 minutes, occasionally scraping bowl. Spoon batter into pan.
Bake at 350*F for 55 to 60 minutes, until toothpick inserted in center of cake comes out clean. Cool cake in pan on wire rack 10 minutes; remove from pan and invert onto rack; peel off waxed paper. Cool completely.
While cake is cooling, prepare chocolate curls:
In heavy 1-qt. saucepan over low heat, heat 5 squares of chocolate until melted, stirring frequently. Spread melted chocolate evenly in jellyroll pan, covering entire bottom of pan. Refrigerate 10 minutes or until chocolate is firm but not brittle.
Holding a teaspoon at angle, scrape the chocolate into curls. With toothpick, transfer curls to another jellyroll pan; refrigerate. Repeat 3 more times to make 4 batches of chocolate curls in all.
In heavy 1 qt. saucepan over high heat, heat 1/2 c. sugar and 3 T. water to boiling, stirring frequently.
Set candy thermometer in place and continue cooking, without stirring, until temperature reaches 240*F
Meanwhile, in small bowl, with mixer at high speed, beat reserved 2 egg whites until soft peaks form; gradually beat in 2 T. sugar until sugar completely dissolves and whites stand in stiff peaks. With mixer at medium speed, pour hot syrup in thin stream into egg whites. Continue beating until bowl feels cool, about 10 minutes.
Beat in remaining 1 c. butter, 2 T. at a time. Beat until frosting is thick and shiny. Stir in 3/4 c. cocoa, 1 t. vanilla, and 1/8 t. salt until well blended.
Place cake on large platter. Spread frosting evenly over side and top of cake. With toothpick, carefully press chocolate curls onto frosting, completely covering cake. Refrigerate if not serving right away. Sprinkle top of cake lightly with confectioners sugar to serve. 16 servings.