- Place dark chocolate in a heat-proof bowl over a saucepan of simmering water to melt, or microwave to melt. Remove from the heat and stir until smooth, then set aside to cool for 10 minutes.
- Stir egg yolks and coffee mixture into the chocolate, then fold in whipped cream.
- In a clean bowl, whisk egg whites until soft peaks form. Fold egg whites into the chocolate mixture.
- Spoon mousse into 4 glasses and refrigerate for 4 hours, or overnight, to set.