Stir together first 3 ingredients in a large heavy saucepan over low heat, and cook, stirring constantly, 8 to 10 minutes or until chocolate melts and mixture is smooth. Remove from heat, and let mixture cool slightly (about 10 minutes).
Whisk together eggs and vanilla in a large bowl. Gradually whisk in melted chocolate mixture until blended and smooth.
Combine flour and next 3 ingredients; whisk into chocolate mixture until blended and smooth.
Pour batter into 3 greased and floured 9-inch round cakepans.
Bake at 325° for 25 to 30 minutes or until a wooden pick inserted in center comes out clean. Cool cake layers in pans on wire racks 10 minutes. Remove from pans, and let cool completely on wire racks.
Spread 1/2 cup plus 2 tablespoons Chocolate Truffle Filling evenly on top of 1 cake layer. Top with 1 cake layer; spread 1/2 cup plus 2 tablespoons Chocolate Truffle Filling evenly on top, reserving remaining 1/2 cup Chocolate Truffle Filling. Top with remaining cake layer.
Microwave coarsely chopped semisweet chocolate squares and cream in a 2-quart microwave-safe bowl at HIGH 1 1/2 to 2 minutes, stirring after 1 minute and then every 30 seconds until chocolate melts and mixture is smooth and slightly thickened. Let cool slightly (about 15 minutes).
Spread warm semisweet chocolate mixture over top and sides of cake. Chill cake 30 minutes or until chocolate glaze is firm. Pipe border using a rosette tip around bottom of cake with remaining 1/2 cup Chocolate Truffle Filling. Sprinkle finely grated semisweet chocolate evenly over top of cake.