01 - Combine chopped dark chocolate and cubed butter in a heatproof bowl set over simmering water. Stir gently until smooth. Remove from heat and set aside to cool slightly.
02 - Whisk egg yolks with half of the granulated sugar until pale and creamy. Incorporate peppermint extract and a pinch of salt.
03 - Gradually whisk the melted chocolate mixture into the egg yolk mixture until fully integrated.
04 - In a clean bowl, whisk egg whites to soft peaks. Slowly add remaining sugar while continuing to beat until stiff, glossy peaks form.
05 - Whip the cold heavy cream to soft peaks in a separate bowl.
06 - Gently fold whipped cream into the chocolate mixture until just combined, maintaining lightness.
07 - Carefully fold the beaten egg whites into the chocolate mixture in two additions, preserving airiness for a light texture.
08 - Spoon the mousse into individual serving glasses or ramekins, cover, and refrigerate for at least 2 hours until fully set.
09 - Optionally garnish with whipped cream, chocolate shavings, and crushed peppermint candies before serving.