01 - Combine crushed cookies with melted butter until evenly mixed. Divide into 4 serving cups and press to form an even layer. Chill while preparing mousse.
02 - Melt dark chocolate gently using a double boiler or microwave, stirring until smooth. Allow to cool slightly.
03 - Whisk egg yolks with sugar and vanilla extract until thickened and pale.
04 - Whip cold heavy cream to soft peaks.
05 - Whisk egg whites with a pinch of salt until stiff peaks form.
06 - Fold melted chocolate into egg yolk mixture until well incorporated.
07 - Gently fold whipped cream into chocolate mixture, then carefully fold in beaten egg whites to maintain airy texture.
08 - Spoon mousse over cookie bases in cups and smooth the tops evenly.
09 - Refrigerate cups for at least 2 hours until mousse is set.
10 - Top with optional whipped cream, chocolate shavings, or fresh berries before serving.