01 - Melt 7 oz dark chocolate in a heatproof bowl over simmering water, stirring until smooth. Brush silicone cupcake molds or paper liners generously with melted chocolate to create a thick, even layer. Chill in refrigerator for 15 minutes, then apply a second coat. Chill until fully set, at least 30 minutes. Peel away molds or liners carefully to release cups.
02 - Melt 7 oz dark chocolate over simmering water and allow to cool to room temperature. Beat egg whites with a pinch of salt until soft peaks form; gradually add sugar and beat until stiff peaks form. Whip heavy cream to soft peaks. Stir egg yolks into cooled chocolate until smooth. Gently fold whipped cream into chocolate mixture, then fold in egg whites in three additions to maintain airiness.
03 - Spoon or pipe mousse into prepared chocolate cups. Chill for at least 2 hours until set.
04 - Optionally, top with whipped cream, fresh berries, or chocolate shavings. Serve chilled.