Combine the chocolate, butter, sugar and coffee in a small heavy saucepan and place over medium-low heat. Stir frequently until the chocolate is just melted and everything is smooth. Remove from the heat, stir in the salt, and transfer to a mixing bowl, and cool to warm room temperature.
In a clean, dry bowl using an electric mixer blend the egg whites on medium-high speed until they form stiff peaks.
Stir the egg yolks and vanilla into the cooled chocolate until well combined. In two batches, fold the egg whites into the chocolate mixture just until combined, but still a little bit streaky. Transfer to 4 individual serving cups or ramekins. Chill for at least 4 hours. Serve chilled with sweetened whipped cream.