Chocolate-Almond Cake with Mousse Filling

For the cake:

1. Roll the almond paste between two sheets of parchment paper into a 9 x 14 inch rectangle. Set aside.
2. Line a jelly roll pan/half-sheetpan with parchment and spray with non-stick spray. Preheat the oven to 350º.
3. In the bowl of an electric mixer fit with the whisk attachment, beat together the egg whites, salt and cream of tartar until just foamy.  Slowly add 1/2 cup of the sugar and beat on high until you achieve stiff peaks but be careful not to over whip otherwise the egg whites will become dry and clumpy and difficult to fold into the remaining ingredients.
4. Transfer the egg whites to a large, clean bowl.
5. Add the yolks, remaining 1/4 cup sugar and vanilla to the mixing bowl in which you beat the egg whites (you needn't clean it after whisking egg whites in it) and whisk on high until the egg yolks are pale yellow and ribbon when you lift the whisk from the batter.
6. Stir 1/3 of the egg whites into the yolk mixture and then gently fold in the remaining egg whites. Sift the cocoa powder over the egg mixture and fold into the batter until just combined. Spread the batter evenly on your prepared jelly roll pan with a large off-set spatula and bake for 25 minutes.
7. Place the rectangle of almond paste onto one end of the cake.  Using the kitchen towel to help you, roll the cake into a jellyroll and allow to cool completely.
8. Using a medium sized bowl (or a 10 inch springform cake pan), cut the jelly roll into 1/3" thick rounds and line your chosen receptacle by dipping one side of each slice quickly into the coffee simple syrup (or amaretto) and line the bowl or springform, starting at the middle, with the jelly roll rounds, placing them soaked side down and tightly together.  Set aside.

For the filling:

1. Place the chocolate in a large mixing bowl and then bring the butter and cream to a simmer in a large saucepan.  Pour the cream/butter mixture over the chocolate and allow to sit for a few minutes undisturbed.  Then stir the mixture gently until the mixture is smooth and totally combined. Note: If you have cake left naked along the sides, make another half batch of ganache to fill it up almost to the edge of the cake.
2. Refrigerate until set. This takes a few hours.
3. Trim edges of the cake even with the filling.  Invert the cake onto a serving platter.  Use a blow dryer or heat gun to gently warm the sides of the bowl or cake pan to release the cake cleanly (but not so much that you melt the filling).

—Recipe adapted from Jimmy Schmidt's London Chop House Chocolate-Almond Cake with Mousse Filling by Gesine Bullock-Prado, Confections of a (Closet) Master Baker