Beat egg yolks until light and fluffy. Add sugar gradually and beat until smooth and light in color. Add lime juice and lemon juice, grated rind and a pinch of salt. Mix until well blended. Stir over low heat until mixture thickens. Soak gelatin in rum and stir into hot custard until it is dissolved. Cool. Oil souffle dish and wrap an oiled paper collar (2" over souffle dish rim) around the top. Beat egg whites until stiff. Whip 1 cup heavy cream until stiff. Fold egg whites into cooled custard, then whipped cream. Pour into souffle dish and chill.
When ready to serve, whip remaining cream. Remove paper collar and decorate top with whipped cream and optional lime slices and crushed pistachios, crystallized violets.