01 - Melt the chocolate in a heatproof bowl over simmering water (double boiler), stirring until smooth. Remove from heat and let cool slightly.
02 - In a clean bowl, beat the egg yolks with 2 tbsp sugar and vanilla extract until thick and pale.
03 - Stir the cooled, melted chocolate into the yolk mixture until well combined.
04 - In another bowl, beat the egg whites with a pinch of salt until foamy. Gradually add the remaining 2 tbsp sugar and beat until stiff peaks form.
05 - In a separate bowl, whip 3/4 cup heavy cream until soft peaks form.
06 - Gently fold the whipped cream into the chocolate-yolk mixture.
07 - Carefully fold in the beaten egg whites in two additions, ensuring the mixture stays light and airy.
08 - Spoon the mousse into individual serving glasses or bowls. Cover and chill in the refrigerator for at least 2 hours, or until set.
09 - For the topping, whip 2/3 cup heavy cream with powdered sugar and vanilla extract until soft peaks form.
10 - Pipe or spoon the whipped cream over the chilled chocolate mousse just before serving.