01 - Melt the chocolate in a heatproof bowl over a saucepan of barely simmering water, stirring until smooth. Remove from heat and let cool slightly.
02 - In a clean bowl, beat the egg whites with a pinch of salt until soft peaks form. Gradually add half the sugar and beat to stiff peaks.
03 - In another bowl, whisk the egg yolks with the remaining sugar and vanilla extract until pale and creamy.
04 - Fold the melted chocolate into the egg yolk mixture until well combined.
05 - In a separate bowl, whip the heavy cream to soft peaks.
06 - Gently fold the whipped cream into the chocolate mixture.
07 - Carefully fold in one-third of the beaten egg whites to lighten the mixture, then gently fold in the remaining egg whites until just combined. Do not overmix.
08 - Spoon the mousse into serving glasses or bowls. Cover and refrigerate for at least 2 hours to set.
09 - Before serving, toss the strawberries with powdered sugar if desired. Top each mousse with strawberries, garnish with mint leaves and chocolate shavings.