01 - Melt chopped dark chocolate in a heatproof bowl set over simmering water, stirring until smooth. Remove from heat and allow to cool slightly.
02 - Beat egg yolks with half of the granulated sugar and vanilla extract until pale and thick.
03 - Gradually add melted chocolate into the egg yolk mixture, stirring continuously to combine thoroughly.
04 - In a separate clean bowl, whip egg whites with a pinch of salt until soft peaks form. Gradually add remaining sugar and continue whipping until stiff peaks develop.
05 - Gently fold whipped egg whites into the chocolate mixture in three additions, maintaining lightness.
06 - Whip heavy cream until soft peaks form and carefully fold it into the chocolate mixture until fully incorporated.
07 - Spoon mousse into four serving glasses or ramekins, cover, and refrigerate for at least 2 hours until set.
08 - Beat chilled heavy cream with powdered sugar and vanilla extract until soft peaks form.
09 - Top each set mousse portion with a generous dollop of whipped cream before serving.