Preheat oven to 350°F.
Butter four round 9-inch cake pans and line with parchment paper. Pulse hazelnuts in food processor until finely chopped (do not allow nuts to form a paste), then stir together with flour in large bowl.
Beat together butter and half the sugar until pale and fluffy. Add yolks one at a time. Beat in Frangelico, and then fold in nut mixture by hand.
In a clean bowl with mixer set on medium speed, beat egg whites with salt until they hold stiff peaks. Add remaining sugar and increase speed until whites hold stiff peaks. Fold in 1/4 of the whites to lighten the batter, then work in the remaining whites gently but thoroughly. Divide the batter into the prepared pans and smooth the tops. Bake until the center is set and the top is pale golden, 15 to 20 minutes. Cool cake in pan on a rack.
To make blackberry coulis: In a heavy saucepan over moderate heat, combine the ingredients and reduce the mixture by one-third. Stir occasionally so the mixture does not scorch. Remove from heat and strain to remove all seeds. Cool the sauce to room temperature.
To make the buttercream frosting: Cream the butter until light and fluffy. Set aside.
Combine sugar, water and corn syrup in a saucepan. Boil to 240°F., brushing down the sides of the pan. Do not stir.
While the syrup is boiling, whip the eggs, egg whites, salt and vanilla on low speed to combine. Remove the syrup from the heat, wait about 10 seconds, then gradually pour the hot syrup into the egg mixture, adding it in a steady stream between the whip and the side of the bowl, with the mixer at medium speed. Increase to high speed and whip until cold.
Reduce to low speed and gradually mix in the whipped butter. Remove the mixing bowl from the machine. Place one-third of the butter mixture in a separate bowl and quickly mix in the melted chocolate to temper. Still working quickly, add this to the remaining buttercream.
To make blackberry mousse: Combine 2 cups of buttercream with 1/2 cup coulis.
To assemble the torte: Remove the parchment paper from the cooled cake layers and place one layer on a serving plate. Using a pastry brush, paint the cake with Frangelico and spread 1/3of the coulis on top. Place the next layer on and paint the cake with Frangelico again. Spread the buttercream over this layer just to the edge of the cake and top with another cake layer. Paint more Frangelico and top with a layer of the blackberry mousse. Finally, to with the last layer of the torte and buttercream. Mask the sides of the torte with hazelnuts and pipe rosettes of mousse on top.
Note: Commercially made buttercream frosting can be substituted.
