Combine chocolate, water, vanilla, and salt in top of a double boiler. Cook over boiling water, stirring constantly, until chocolate melts.
Beat egg yolks in a small mixing bowl until thick and lemon colored. Gradually stir one-fourth of hot chocolate mixture into egg yolks; add to remaining hot chocolate mixture, stirring constantly. Continue cooking, stirring constantly, 2 minutes or until mixture thickens. Set aside to cool.
Beat egg whites (at room temperature) in a medium mixing bowl until soft peaks form. Gradually add 1/4 cup sugar, 1 tablespoon at a time, beating until peaks are stiff and glossy. Fold meringue and 1 1/2 cups whipped cream into cooled chocolate mixture. Pour into ten 6-ounce stemmed glasses, and refrigerate until set. Garnish each mousse with sweetened whipped cream and chocolate curls before serving.