01 - Set a heatproof bowl over a pan of simmering water to create a double boiler. Add chopped chocolate and butter cubes, stirring continuously until completely smooth and melted. Remove from heat and allow to cool for 5 minutes.
02 - In a large mixing bowl, whisk egg yolks with half the sugar (2 tbsp) and vanilla extract until the mixture becomes pale yellow and creamy. Gradually pour in the cooled chocolate mixture while whisking constantly until fully incorporated.
03 - Using a clean, dry bowl, beat egg whites with a pinch of salt until soft peaks form. Slowly add the remaining sugar and continue beating until stiff, glossy peaks form—this creates the signature airy texture.
04 - In a separate chilled bowl, whip the cold heavy cream until soft peaks form. Be careful not to overwhip as the cream should remain foldable.
05 - Gently fold one-third of the whipped cream into the chocolate mixture to lighten it. Add the remaining cream and fold using a rubber spatula with a figure-eight motion until just combined.
06 - Add the beaten egg whites in three separate additions, folding gently after each addition. Use light, sweeping motions to maintain the air structure—stop when no white streaks remain.
07 - Spoon or pipe the mousse into individual serving glasses or ramekins, filling about 3/4 full. Refrigerate for at least 2 hours or until completely set and firm to the touch.
08 - Just before serving, top each mousse with fresh berries, a scattering of chocolate shavings, and a small mint sprig. Serve chilled with crisp butter cookies or ladyfingers on the side.