In a heatproof bowl set over a pot of simmering water, melt the chopped dark chocolate.
Stir until smooth.
Remove from heat and let it cool slightly.
In a separate bowl, whisk the egg yolks, sugar, and vanilla extract until creamy.
Gradually pour the melted chocolate into the egg yolk mixture, stirring until well combined.
In another bowl, whip the heavy cream until soft peaks form.
In a clean bowl, beat the egg whites until stiff peaks form.
Gently fold the whipped cream into the chocolate mixture until no streaks remain.
Then, fold in the beaten egg whites until the mixture is light and airy.
Divide the chocolate mousse into serving dishes.
Cover and refrigerate for at least 2 hours, or until set.
Before serving, top the chocolate mousse with whipped cream, chocolate shavings, or fresh berries.
Enjoy!