I made my own alterations to the recipe the second time around that I made this. I added 2 teaspoons of vanilla to the chocolate and yolks while mixing, I also added 2 teaspoons of vanilla and 2 teaspoons of sugar to the eggs whites while beating them at high speed. Additionally I added 1.5 teaspoons of vanilla and 2 teaspoons of sugar to the whipping cream. I know this may seem like overkill but the sugar and light flavour of the vanilla complimented the bittersweet dark flavour of the chocolate.
Find the recipe here!