Make the cake. Preheat the oven to 350 F.
Grease the pan with butter and sift with the flour.
Chop the chocolate. Place it in a bowl and melt it in a microwave. Let it cool. Whip the egg yolks with the sugar until they are light and pale. Cut the butter into pieces and incorporate into the egg yolks mixture. Whip on low speed using a mixer. Pour the chocolate and stir. Then add the cognac and the almond flour, stir again. Whip the egg whites until stiff peaks form. Then gently fold a little of the beaten egg whites into the batter to lighten it, and then add the rest of the whites, folding just until incorporated. Do not over mix the batter or it will deflate! Pour the mixture into a spring cake form or cake ring 7-inch diameter. Bake for 35-40 minutes or until a skewer comes out clean. Remove the cakes from the oven and allow to cool a little before removing from the tins and transferring to wire racks to cook completely.
Make the chocolate mousse. Whip the cream in a cold bowl until medium peaks. Place in the refrigerator until uses.
In a saucepan combine water and the sugar and bring to boil, brushing down sides of pot as necessary with a pastry brush dipped in water. Cook until sugar syrup registers 248°F (or 120°C) on an instant read or candy thermometer.
Meanwhile, start whipping the egg with the egg yolk. Set mixer to low speed and mix until soft peaks form. With the mixer running, carefully and slowly drizzle in hot sugar syrup. Increase speed to high and whip until desired stiffness is achieved, about 5 minutes.
Chop the chocolate. Place it in a bowl and melt it in a microwave. Let it cool to 104°F-113°F (40-45°C)
Gently fold a little of the whipped cream into the chocolate, and then add the rest of the cream. Then gently fold it into the egg mixture and gently stir just until incorporated.
Cut the cake into 2 discs. Place the first disc on a piece of cardboard (or parchment paper) cut in an 7-inch circle. Using a pastry brush, brush the disc with the cognac. Coat the cake with a 2/3 of chocolate mousse. Place the second disc on top and gently press on it then cover the rest mousse.
Place the cake in the refrigerator for 2-3 hours or overnight.
Make the ganache. Chop the chocolate. In a saucepan combine the chocolate and the butter. Heat over low-medium heat stirring constantly until everything is melted and incorporated. Remove from the heat and let it cool. Then pour the ganache on the top of the cake and let it flow randomly. Now you can serve it. Enjoy!