Decadent Chocolate Mousse Cake (Longhorn Steakhouse Chocolate Mousse Cake)

• Prepare a 9 x 13 inch cake as directed on the label of the cake mix box.
• Bake and let it cool slightly in the pan. Invert onto a rack to cool completely.
• Cleaning out the used cake pan, line it with plastic wrap.
• Cut the cake in half lengthwise, and then in thirds crosswise, making 6 rectangles.
• Slice each rectangle in half to make two layers, using a serrated knife.
• Arrange half of the pieces snugly in the cake pan.
• Crumble the remaining pieces and press tightly into 6 small balls.
• Arrange 1 cake ball in the center of each cake rectangle in the pan.

To make the mousse

• In a heatproof bowl set over a saucepan of simmering water, heat the chocolate, butter, coffee and ¼ cup water. Do not let the bowl touch the water. Stir often, until melted.
• After removing the bowl from the pan, stir until cooled off.
• Reserve the simmering water.
• Fill a large bowl with ice water.
• Mix the egg yolks, 1 ½ cups sugar and 2 tablespoons water in a separate large heatproof bowl, using a whisk.
• Place this bowl over the saucepan of simmering water, whisking for 6 to 8 minutes, or until pale yellow.
• Pour in the chocolate-coffee mixture and the vanilla. Mix with a whisk about 2 minutes, or until combined.
• Remove the bowl from the pan and set in the bowl of ice water.
• Whisk for about 4 minutes or until slightly cool but not thick.
• Using a mixer, beat the egg whites and salt in a bowl until foamy.
• Adding 2 tablespoons of sugar, beat until almost stiff.
• Gently fold into the chocolate-yolk mixture to make a dark chocolate mousse.
• Spread 5 cups over the cake and cake balls.
• Freeze for about 30 minutes or until firm on top.
• Beat the heavy cream and the remaining 4 tablespoons sugar until soft peaks form.
• Fold this mixture into the remaining mousse.
• Remove the cake from the freezer.
• Spread with the light chocolate mousse.
• Cover with plastic wrap and freeze at least 6 hours or overnight, until firm.

To make the chocolate shell

• In a heatproof bowl set over a saucepan of simmering water, stir the chocolate, heavy cream and 4 tablespoons corn syrup, until melted. Do not let the bowl touch the water. Spread half of the shell mixture over the frozen mousse, a spoonful at a time. Return to the freezer.
• Add the remaining 1 tablespoon corn syrup and the butter to the remaining chocolate shell mixture. Put in microwave 30 seconds. Stir until glossy.

To make the chocolate sauce

• For serving the cake, beat the heavy cream with a mixer until foamy. Add the sugar and beat until soft peaks form. Remove the cake from the freezer. Invert it onto a baking sheet and unmold. Invert again onto a platter, with the chocolate shell-side up.
• Using a warm knife, cut the cake in half lengthwise. Then cut into thirds crosswise to make 6 rectangles. Cut each rectangle in half diagonally to make 2 triangles.
• Top each triangle with whipped cream, ice cream and the prepared chocolate sauce.