Melt the Chocolate: Start by breaking the dark chocolate into pieces and melting it gently in a heatproof bowl over a pot of simmering water. Stir it until completely melted and smooth. Remove from heat and set aside to cool slightly.

Beat the Egg Yolks: In a separate bowl, whisk the egg yolks and sugar together until they become pale and creamy. This should take about 3 to 5 minutes.

Combine Chocolate and Yolks: Slowly pour the melted chocolate into the egg yolk mixture, stirring gently until fully combined. Add in the vanilla extract and a pinch of salt to enhance the flavor.

Whip the Cream: In another bowl, whip the heavy cream until soft peaks form. You want it fluffy, but not too stiff.

Whisk the Egg Whites: In a clean bowl, whisk the egg whites until they form stiff peaks. This may take about 4 to 5 minutes.

Fold It Together: Gently fold the whipped cream into the chocolate mixture until combined. Then, add the egg whites gradually, folding carefully to keep the airy texture.

Chill: Pour the mousse into serving dishes and refrigerate for at least 2 hours, allowing it to set and develop its deep chocolate flavors.

Serve and Enjoy: Top with additional whipped cream or berries, if you like, and serve chilled to enjoy each indulgent bite!