Melt the dark chocolate and butter together until smooth.
Let the chocolate mixture cool slightly.
Whisk the egg yolks into the cooled chocolate one at a time.
Stir in the vanilla extract.
Beat the egg whites with the salt until foamy.
Gradually add the sugar while beating until stiff peaks form.
In a separate bowl, whip the heavy cream until soft peaks form.
Fold the whipped cream gently into the chocolate mixture.
Carefully fold in the beaten egg whites in batches.
Spoon the mousse into serving glasses or bowls.
Refrigerate for at least 4 hours or overnight.
Garnish with chocolate shavings and fresh raspberries before serving.
