01 - Combine dark chocolate and butter in a heatproof bowl over simmering water; stir until smooth. Remove from heat and allow to cool slightly.
02 - In a large bowl, whisk egg yolks with half of the sugar (1.1 oz) until pale and creamy.
03 - Gently fold the melted chocolate mixture into the egg yolk blend until well combined.
04 - In a clean bowl, whisk egg whites with a pinch of salt until soft peaks form; gradually add remaining sugar (1.1 oz) and continue whisking to stiff, glossy peaks.
05 - Fold one-third of the egg whites into the chocolate mixture to lighten it, then gently fold in the remaining whites in two additions without deflating.
06 - Whip chilled heavy cream until soft peaks form, then fold it gently into the chocolate mixture until smooth and homogeneous.
07 - Divide the mixture into serving glasses or ramekins, cover, and refrigerate for at least 2 hours until set.
08 - Optionally garnish with chocolate shavings, fresh berries, or whipped cream before serving.