To prepare the chocolate cake: preheat the oven to 375 degrees F.
Butter 4 (12 by 18 by 1/2-inch) baking sheets, line with parchment paper and butter paper.
In a mixing bowl, combine the egg yolks and granulated sugar. Cook over a double boiler while whisking until triple in volume, and until the mixture reaches 110 degrees F.
In another mixing bowl, beat the egg whites until soft peaks. Add the powdered sugar, a little at a time, and continue to beat until stiff but still shiny. Whisk 1/4 of the meringue into the egg yolk mixture. Gently fold the remaining meringue into the mixture.
Combine the flour, cocoa, almond meal and salt. Sift and gently fold into the egg mixture, a little at a time. Divide evenly into the 4 buttered baking sheets and with an offset spatula, spread evenly. Bake for 10 to 12 minutes or spongy and cooked. Reserve and allow to cool completely.
To prepare the Coffee Syrup: in a saucepan, bring the water and sugar to a boil for 2 minutes. Turn off heat and stir in instant espresso. Reserve until needed.
To prepare the Chocolate Mousse: in a saucepan, bring the water and sugar to a boil. Lower to a simmer and reserve. In a mixing bowl, using a whisk, whip the egg yolks on high speed until light and ribbony. Lower the speed and whisk in the hot syrup. Continue to beat until slightly cool. Fold in the melted chocolate and lastly, fold in the whipped cream. Reserve until needed.
To assemble the 16 layer cake: Cut each cake into 2 pieces horizontally. Place the first layer on a piece of cardboard. Brush with some of the coffee simple syrup. Spread 1/8 of the chocolate mousse evenly over the cake. Top with another layer of genoise and repeat the process until you have 8 layers of genoise brushed with coffee simple syrup and chocolate mousse. Chill for 2 hours.
Trim off about 1/4-inch from all the sides with a serrated knife that has been dipped in hot water. Pour the ganache over the top of the cake, and using an offset spatula, spread the ganache to evenly cover the top and sides of the cake. Refrigerate for 20 minutes, or until the chocolate hardens. Dust the top with cocoa powder.
2 cups heavy cream
10 ounces bittersweet chocolate, chopped
Bring the cream to a simmer in a heavy saucepan. Place the chocolate in a heatproof bowl. Pour the cream over the chocolate and whisk until the mixture is smooth. Cool slightly.