Melt the chocolate in a double boiler or a bowl set over a pan of simmering water. When just melted, remove from heat and add the sugar and coffee. Cool slightly. Add egg yolks one at a time. Beat egg whites until very stiff peaks are formed. Gently fold egg whites into chocolate mixture. This takes a few minutes. Fold…do not rush! Pour mousse into individual ramekins or stem ware. Refrigerate overnight.