This is a most delicious cake that I found on a food blog Also All the Crumbs Please.  It is a multi-step process and requires extra time for chilling, so I should suggest beginning the day before.  The most challenging part of the recipe is making the mousse and working with the egg yolks to temper them without scrambling them to make the mousse. The result is a chocolate lovers dream cake and makes for a beautiful presentation.  I recommend using a high quality chocolate.  I garnished my cake with a variety of fresh berries and mint rather than extra chocolate shavings, but you can be quite creative with the garnish.  You can go to Also All The Crumbs Please for the recipe