With an electric mixer with whisk attachment, whip the heavy cream in a large bowl until stiff peaks form.
In another bowl, mix together the condensed milk, marshmallow fluff, vanilla extract and salt. Gently fold the condensed milk mixture into the whipped cream until just combined.
Transfer to a 9x5 loaf pan and freeze for at least 6 hours.
Notes
Keep your bowl in the freezer for 15 minutes and use really cold heavy cream to get good whipped cream.
If you want lower fat ice cream, replace the heavy cream with half-and-half and use fat-free sweetened condensed milk.
Freeze for at least 6 hours so the ice cream has time to freeze and won't melt.