For a decadent chocolate torte, bake genoise in a sheet pan and quarter it -- then layer the pieces with two kinds of mousse and top with chocolate shards.
Sprinkle 1 teaspoon gelatin over 2 tablespoons water in a heatproof bowl. Sprinkle remaining 1/2 teaspoon gelatin over 1 tablespoon water in another heatproof bowl. Let soften about 3 minutes.
Bring sugar and 1/2 cup water to a boil in a medium saucepan over high heat. Swirl pan to dissolve sugar. Wash down sides of pan with a wet pastry brush to prevent crystals from forming. Boil until sugar turns dark amber, about 10 minutes. Remove from heat. Slowly add 1 cup cream and the butter, stirring until butter has melted. Put 2/3 cup caramel into a medium bowl; set aside. Stir remaining caramel and the unsweetened chocolate in another medium bowl; set aside.
Set 1 bowl of softened gelatin over a pan of simmering water, and stir until gelatin has melted. Repeat with remaining bowl of gelatin. Pour larger batch of gelatin into plain caramel. Pour smaller batch of gelatin into chocolate caramel. Let cool completely, stirring occasionally, 10 to 12 minutes.
Whisk remaining 1 1/4 cups cream in a medium bowl until stiff peaks form. Fold one-third of the whipped cream into plain caramel mixture; fold remaining whipped cream into chocolate-caramel mixture. Refrigerate the mousses until slightly firm, about 10 minutes. Stir almond praline into plain caramel mousse.
Stir Cognac and simple syrup in a small bowl. Assemble torte: Place 1 cake rectangle on a platter; brush with one-quarter of the Cognac syrup. Spread with half the chocolate-caramel mousse. Top with another cake rectangle; brush with one-quarter of the syrup. Spread with praline-caramel mousse. Refrigerate 10 minutes to set. Top with another cake rectangle; brush with one-quarter of the syrup. Spread with remaining chocolate-caramel mousse. Top with remaining cake rectangle; brush with remaining syrup. Clean edges with an offset spatula. Refrigerate until firm, about 30 minutes. Sprinkle with bittersweet chocolate shavings.