Start by chopping the dark chocolate into small pieces and melting it gently over a double boiler or in the microwave in short bursts (10-15 seconds), stirring frequently until completely smooth. Set aside to cool slightly.

In a large mixing bowl, pour in the heavy cream and whip it using an electric mixer until soft peaks form. Be careful not to over-whip.

In another bowl, separate the egg whites from the yolks. Whisk the egg yolks with sugar until creamy and pale. Add in the melted chocolate and vanilla extract, stirring until fully combined.

Gently fold the whipped cream into the chocolate mixture until no streaks remain. In a separate clean bowl, beat the egg whites with a pinch of salt until stiff peaks form and carefully fold them into the chocolate mixture.

Spoon or pipe the mousse into mini cups or dessert glasses. Refrigerate for at least 2 hours to set. Top with additional whipped cream or your favorite fruits just before serving.