Place a 9x5-inch loaf pan in the freezer to chill.
To the bowl of a stand mixer, add the heavy cream. Start mixing at the lowest speed, and then gradually increase speed to medium until the cream starts to get thicker. (The gradual progression prevents you from spraying yourself with cream.)
The cream will thicken and start to peak. Mix on high speed until the cream is thick and stiff. This happens quickly, so watch it closely!
In a separate medium bowl, combine sweetened condensed milk, vanilla, and salt, and 1 cup of whipped cream from the stand mixer. Stir to incorporate this sweetened condensed milk mixture.
Gently fold the sweetened condensed milk mixture back into the mixing bowl with the rest of the whipped cream.
Pour the mixture into the chilled pan and then cover with plastic wrap or parchment paper. Freeze for at least 5 hours, or until fully set up, before serving.
