Toast the hazelnuts in the oven and remove the outer skins. Melt 1 Tablespoon of the sugar in a small saucepan and add the toasted hazelnuts to it. Process or pound this combination to a smooth hazelnut paste. Melt 3oz/85g of the unsweetened chocolate and set aside. Whisk together the 6 eggs, 3 egg yolks, and all but 1 Tablespoon of the remaining sugar until foamy and thick. Do this with the bowl standing over a saucepan full of warm water; don't allow the water to get any more than body temperature, or the cake will be spoiled. Add the honey, remove from the heat, and continue to beat until completely cool and thickened. Place the butter, melted chocolate, vanilla, and hazelnut paste in another bowl over a pan full of hot water or in the top of a double boiler and stir until smoothly mixed together. Sift the flour and cake flour into the egg, sugar and honey mixture and fold in very carefully and gently. Then fold in the chocolate-hazelnut mixture. Pour this into two buttered and floured 23 cm/23cm cake pans and place in a preheated 190C/375F oven. Bake for about 40 minutes. When the cakes are done, lift out of the oven and turn out onto a clean cloth, where they can be left to cool. Put the remaining 5oz/140g unsweetened chocolate in a bowl over a pan of hot water or in the top of a double boiler, add the cream, and stir until smooth. As soon as it begins to boil, remove from the heat and pour into a bowl to cool, stirring occasionally to prevent a skin from forming on the top. Put the apricot jam in a small saucepan and add the remaining 1 Tablespoon sugar. Stir over low heat until melted, then set aside in a warm place. Melt the sweetened chocolate and also set aside in a warm place. Whip the cream and chocolate mixture until stiff. Place the cooled cakes on a serving platter with a sheet of wax paper underneath. Slice off the hard crust. Mix the liqueur with the brandy and paint half of it all over one of the cakes. Spread three-quarters of the chocolate cream over the same cake, then put the other cake on top, so that the two form a single cake. Paint the top of the cake with the remaining liqueur, then coat the cake completely with apricot jam. Spread with the sweetened chocolate and decorate with the remaining chocolate cream. Remove the wax paper before serving. Do not put the cake in the refrigerator, but keep it in a cool place until ready to serve. This cake is traditionally baked in a round pan and has "Gianduja" or "Gianduia" written across it with melted chocolate.

Viviane's Note: If you cannot get unsweetened chocolate, substitute bittersweet chocolate and reduce the amount of sugar. I would maybe use about 0.75 cup of sugar (half the suggested amount) but it depends on how sweet you like it to be.