Preheat oven to 325°F.
Grease bottoms and sides of 2 round 9 X 1 1/2-inch cake pans with shortening. Line bottom of pans with waxed paper or cooking parchment paper.
Place chocolate chips and butter in heavy 2-quart saucepan. Place pan over medium heat and melt chocolate, stirring constantly, about 5 minutes.
Add flour. Stir to mix until smooth.
Add egg yolks. Whisk until well blended.
Place egg whites in large bowl. Beat with electric mixer on high speed until foamy.
Add sugar while beating, 1 tablespoon at a time, until soft peaks form.
Fold chocolate mixture into egg whites.
Fold in toasted hazelnuts.
Spread batter in pans.
Place in preheated oven and bake about 25 minutes or until tops of cakes appear dry and toothpick inserted in center comes out clean.
Remove from oven and cool 5 minutes.
Run a knife around the side of each cake to loosen. Remove from pans to wire rack. Remove waxed paper.
Cool completely.
While cakes are cooling, prepare Chocolate Truffle Filling and Chocolate Ganache according to the recipes in boxes below.
Spread 2/3 cup of the filling on top of one cake.
Top with other cake.
Frost top and sides of cake with remaining filling.
Drizzle with chocolate ganache allowing it to run and drip down sides.
Serve.