Melt chocolate in a double boiler or in a pan with hot water. Add sugar, coffee and egg yolks, one at a time. Stir until mixture has thickened. Remove from heat. Let cool. Whip cream. Add to slightly cooled chocolate mixture. Spoon mousse into individual serving dishes. Cover. Let cool in refrigerator for 1 hour. Garnish each serving with a spoonful of whipped cream.