Begin by breaking the dark chocolate into small pieces and place it in a heatproof bowl. Melt the chocolate gently using a microwave in 30-second intervals or over a pot of simmering water (bain-marie). Once melted, set aside to cool slightly.

In a separate mixing bowl, whisk the egg yolks and 2 tablespoons of sugar together until the mixture turns pale and creamy. Stir in the melted chocolate and vanilla extract until well combined.

In another clean bowl, whip the heavy cream using an electric mixer or a whisk until soft peaks form. Gently fold the whipped cream into the chocolate mixture using a rubber spatula. Be careful not to deflate the cream.

In a small bowl, whisk the egg whites with a pinch of salt until they form soft peaks. Gradually add the remaining tablespoon of sugar and continue to whisk until stiff peaks form.

Gently fold the egg whites into the chocolate-cream mixture in three parts, ensuring not to lose the airiness of the egg whites. The mixture should remain light and fluffy.

Once fully combined, spoon the mousse into serving dishes or cups. Cover with plastic wrap and refrigerate for at least 2 hours to set.

Serve chilled and enjoy your delicious chocolate mousse!