Heat the chocolate in a small pot in a water bath. Slowly add the coffee after the chocolate melts. The egg yolks need to be beaten in advance. Add them to the chocolate and coffee - slowly, while stirring continuously in a clockwise direction.
In a separate bowl, mix the cream and sugar and beat them into snow. To this mixture, gradually add the melted chocolate. Distribute the chocolate mousse into dessert cups.
Decorate as desired and allow to harden for 2 hours in the refrigerator. Garnish with biscotti and serve chilled.