Melt the baking chocolate in a double boiler over medium heat. While the chocolate is melting, dissolve the sugar to the hot coffee. Once the chocolate is melted, stir in the coffee mixture and cook over low heat for 5 minutes. Wisk in the egg yolks, one at a time. Mix thoroughly. Remove from the heat and add the dark rum. Set aside. Add a pinch of salt to the egg whites and beat until stiff peaks form. Fold the egg whites into the chocolate mix, gently but thoroughly. Pour into a glass serving dish, or individual dessert dishes. To set the mousse, refrigerate for several hours or overnight. To serve, top with whipped cream.
Recipe courtesy of About.com.