Steps
1. Melt the dark chocolate in a heatproof bowl over simmering water, stirring until smooth.
2. In another bowl, combine the brewed coffee and sugar, mixing until dissolved.
3. Once the chocolate is melted, remove it from heat and stir in the coffee mixture.
4. In a separate bowl, whisk the egg white with a pinch of salt until soft peaks form.
5. In another bowl, whip the heavy cream until soft peaks form.
6. Gently fold the whipped cream into the chocolate mixture, then fold in the egg white until fully combined.
7. Spoon the mousse into serving dishes and chill in the refrigerator for at least 2 hours before serving.