Bring cream and butter to a simmer in a 3- to 4-quart heavy saucepan, then reduce heat to low. Whisk in chocolate until smooth and remove from heat. Transfer ganache to a bowl and chill, covered, stirring every 30 minutes, until thickened but spreadable, about 2 hours. (If ganache becomes too stiff, let stand at room temperature until slightly softened.)
Place rack in middle of the oven. Preheat oven to 350 degrees. Butter three 8-by-2-inch round cake pans. Line with parchment paper. Butter the parchment, and dust with cocoa powder; tap out excess. Sift cocoa; whisk in boiling coffee and milk. Let cool. Sift together cake flour, baking soda, and salt. Set aside.Using a rubber spatula, mix the butter in a large bowl until light and fluffy, about 2 minutes. Gradually add sugar and vanilla. Add the eggs one at a time, stirring well after each addition. Pour in the cooled cocoa mixture. Mix until fully incorporated. Add the sifted dry ingredients to the chocolate mixture, stirring until just combined.
Pour the batter into the prepared pans. Bake for around 20 minutes, then rotate the pans, and bake for an additional 15 minutes, until a cake tester comes out clean when inserted into the center. Remove the cakes from the oven, and allow to cool in pans for 15 minutes on a cooling rack. Carefully run a small offset spatula around the edge of the cakes to loosen them from the pan. Remove cakes from pans, and invert onto a wire rack. Let cool completely, about 1 hour.
Make mousse and assemble torta:
Melt butter and chocolate in a double boiler or a metal bowl set over a saucepan of barely simmering water, stirring until smooth, and stir in Cognac. Transfer to a bowl and chill, covered, stirring occasionally, until thickened to the consistency of softened butter, about 1 hour. (If mixture becomes too stiff, let stand at room temperature until softened.)
Beat cream in a bowl with cleaned beaters until it just holds soft peaks, then chill, covered, while beginning to assemble torte.
Put 1 cake layer on cardboard round on a rack set in a shallow baking pan (1 inch deep). Spread 1/2 cup ganache evenly over top of layer and sprinkle with all of chopped Hazelnuts.
Beat egg whites with a pinch of salt using cleaned beaters at medium-high speed until they just hold soft peaks. Add sugar and beat at high speed until whites just hold stiff peaks. Stir whipped cream into chocolate frangilico mixture, then stir in one third of whites to lighten. Fold in remaining whites gently but thoroughly. Spoon mousse immediately onto cake layer (it sets quickly), spreading evenly, then top with third cake layer. Chill torte, covered, until mousse layer is firm, about 1 hour. Keep remaining ganache at a spreadable consistency at room temperature, chilling, covered, if it becomes too soft.
Frost with melted ganache and decorate with cookies, hazelnuts, apricots (made to look like flowers), and top with chocolate shavings.