01 - Combine dark chocolate and butter in a heatproof bowl set over simmering water using a double boiler. Stir until smooth, then remove from heat and allow to cool slightly.
02 - Whisk egg yolks with sugar in a medium bowl until pale and creamy. Incorporate vanilla extract, orange zest, and orange juice. Add the melted chocolate mixture and blend thoroughly.
03 - In a clean bowl, beat egg whites with a pinch of salt until stiff peaks form.
04 - Whip the heavy cream separately until soft peaks develop.
05 - Gently fold one-third of whipped egg whites into the chocolate mixture to lighten it. Carefully fold in the remaining egg whites in two additions, followed by the whipped cream, until fully incorporated and no streaks remain.
06 - Spoon or pipe the mixture into serving glasses or ramekins. Cover and refrigerate for a minimum of 2 hours until set.
07 - Optionally, garnish with additional orange zest, chocolate curls, or a dollop of whipped cream before serving.