Step 1

Prepare a 9 x 13 inch cake as directed on the label of the cake mix box.

Step 2

Bake and let it cool slightly in the pan. Invert onto a rack to cool completely.

Step 3

Cleaning out the used cake pan, line it with plastic wrap.

Step 4

Cut the cake in half lengthwise, and then in thirds crosswise, making 6 rectangles.

Step 5

Slice each rectangle in half to make two layers, using a serrated knife.

Step 6

Arrange half of the pieces snugly in the cake pan.

Step 7

Crumble the remaining pieces and press tightly into 6 small balls.

Step 8

Arrange 1 cake ball in the center of each cake rectangle in the pan.

Step 9

To make the mousse: In a heatproof bowl set over a saucepan of simmering water, heat the chocolate, butter, coffee and 1/4 cup water. Do not let the bowl touch the water. Stir often, until melted.

Step 10

After removing the bowl from the pan, stir until cooled off.

Step 11

Reserve the simmering water.

Step 12

Fill a large bowl with ice water.

Step 13

Mix the egg yolks, 1 1/2 cups sugar and 2 tablespoons water in a separate large heatproof bowl, using a whisk.

Step 14

Place this bowl over the saucepan of simmering water, whisking for 6 to 8 minutes, or until pale yellow.

Step 15

Pour in the chocolate-coffee mixture and the vanilla. Mix with a whisk about 2 minutes, or until combined.

Step 16

Remove the bowl from the pan and set in the bowl of ice water.

Step 17

Whisk for about 4 minutes or until slightly cool but not thick.

Step 18

Using a mixer, beat the egg whites and salt in a bowl until foamy.

Step 19

Adding 2 tablespoons of sugar, beat until almost stiff.

Step 20

Gently fold into the chocolate-yolk mixture to make a dark chocolate mousse.

Step 21

Spread 5 cups over the cake and cake balls.

Step 22

Freeze for about 30 minutes or until firm on top.

Step 23

Beat the heavy cream and the remaining 4 tablespoons sugar until soft peaks form.

Step 24

Fold this mixture into the remaining mousse.

Step 25

Remove the cake from the freezer.

Step 26

Spread with the light chocolate mousse.

Step 27

Cover with plastic wrap and freeze at least 6 hours or overnight, until firm.

Step 28

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.

Step 29

To make the chocolate sauce - Add the remaining 1 tablespoon corn syrup and the butter to the remaining chocolate shell mixture. Put in microwave 30 seconds. Stir until glossy.

Step 30

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.

Step 31

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.

Step 32

Top each triangle with whipped cream, ice cream and the prepared chocolate sauce.