To make the syrup: Stir the syrup ingredients over medium heat until the sugar dissolves. Bring to a full rolling boil, remove from the heat, and set aside to cool., To make the filling: Combine the mascarpone and heavy cream in a large bowl and whisk at low speed until the mixture is smooth. Whisk together the confectioners' sugar and ClearJel, and slowly add to the mixture, followed by the amaretto. Increase speed to medium-high and whisk until medium peaks form., To assemble the cake: Remove the top (browned) crust from the cake. Cut the remaining cake in half horizontally (around the equator) to make two round layers. Place one layer onto a baking sheet that's been lined with a piece of parchment or wax paper., Sprinkle the cake with 3 tablespoons of the syrup. Spread 2 cups of filling onto the cake. Top with the second layer. Sprinkle with 2 tablespoons syrup; let sit for several minutes, then top with the remaining filling., Refrigerate the cake for several hours, so the filling can set completely., When ready to serve, carefully move the cake to a large plate or serving platter. Garnish with cocoa and/or chocolate shavings. Serve cold; refrigerate any leftovers.