Preheat oven to 350º F.

In a large mixing bowl bring egg whites to room temperature. Meanwhile, grease and flour a 9-inch round baking pan. In a medium saucepan melt the butter and semisweet chocolate over low heat, stirring occasionally; cool. Stir in egg yolks and vanilla. Set pan and chocolate mixture aside.

Beat egg whites with an electric mixer on medium to high speed till soft peaks form. Gradually add sugar, about 2 tablespoons at a time, beating on high speed about 4 minutes or till stiff peaks form. Gently fold about 1 cup of the egg white mixture into the egg yolk mixture. Then fold egg yolk mixture into remaining egg white mixture. Sift flour over egg mixture; gently fold in. Do not overfold.

Spread batter into prepared pan. Bake in for about 35 minutes or until a wooden toothpick inserted near center comes out clean. Cool in the pan on a wire rack for 10 minutes. Remove cake from pan; completely cool cake on the wire rack.

To assemble; cut cake horizontally into two even layers. Press apricot preserves through a sieve. Place first cake layer on a serving platter. Spread preserves on top. Top with second cake layer. Spoon Sacher Torte Chocolate Glaze over cake. If desired, garnish with chocolate leaves. Serve with whipped cream. Yield: 12 servings.

Sacher Torte Chocolate Glaze : In a saucepan heat 2 ounces semisweet chocolate, cut up, and 2 Tablespoons butter over low heat just till melted, stirring occasionally. Remove from heat. Stir in ¾ cup sifted powdered sugar and 4 teaspoons hot water till smooth. If necessary, stir in additional hot water to make of drizzling consistency. Makes ½ cup.