until smooth, scraping bowl with rubber spatula; set aside. Add coffee and boiling water to softened gelatin; stir mixture into stiff chocolate mixture scraping bowl constantly, until smooth. Beat in 1-1/2 tsp vanilla and the rum. Transfer mixture to 4-quart bowl; place in large bowl of ice and cold water. Stir, scraping bottom and sides 2-3 minutes or until very cold but not thick. Remove from water temporarily; set aside. In large bowl beat whites with salt until foamy. Gradually beat in remaining 1/2 cup sugar until soft peaks form. Return bowl of chocolate mixture to ice water; stir 2-3 minutes or until mixture barely starts to thicken. Remove bowl from ice water. Fold half the mixture into whites, then fold into remaining mixture (do not overfold). Pour gently from one bowl to another to insure thorough blending. Refrigerate 8-10 hours or overnight. To unmold: since most loaf pans flare, corners probably will not be lined with wax paper. With small, sharp knife loosen corners. Invert flat platter over loaf pan; invert pan over platter. Remove pan; gently peel way paper. Whip creamwith confectioner's sugar and remaining 1 tsp vanilla to thick saucelike consistency. (If desired, whip about 1/2 cup of the heavy cream until stiff. Pipe on mousse to garnish.) Spoon generously over each slice of mousse. Makes 10 servings.