01 - Melt chopped dark chocolate in a heatproof bowl over simmering water, stirring until smooth. Remove from heat and allow to cool slightly.
02 - Beat egg yolks with half the sugar and vanilla extract until pale and thick.
03 - Gradually stir melted chocolate into the egg yolk mixture until fully incorporated.
04 - Whip egg whites with a pinch of salt until soft peaks form. Slowly add remaining sugar and continue beating until stiff peaks develop.
05 - Gently fold whipped egg whites into the chocolate mixture in three additions, preserving airiness.
06 - Whip heavy cream to soft peaks and carefully fold into the chocolate mixture until smooth.
07 - Divide the mousse evenly 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 with a generous dollop of whipped cream before serving.