Heat 2/3 whipped cream until it starts steaming and becomes runny over low flame
In a seperate bowl, Whisk together the egg yolks and sugar
Add half the portion of the hot cream an whisk it till thotoughly combined
Add this egg - cream mixture to the remaining hot cream and keep it on the stove over low flame and cook till before the egg just begins to scramble and keep whisking it completely. Otherwise the egg starts getting scrambled.
remove from heat and add he melted chocolate and vanilla essence and stir till thoroughly mixed.
Chill this chocolate custard completely.
Beat the remaining cream and start adding to the chilled chocolate custard.
Chill the mousse and then serve it with either grated chocolate or top it with fresh berries or whipped cream.