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