Place a 9×5-inch loaf pan in the freezer to chill.
To the bowl of a stand mixer fitted with the whisk attachment, add heavy cream. Start mixing at the lowest speed, and then gradually increase the speed to medium until the cream starts to get thicker. (The gradual progression prevents you from spraying yourself with cream.)
The cream will start to thicken. Mix on high speed until the cream forms stiff peaks.
In a separate medium bowl, combine sweetened condensed milk, vanilla, salt, and 1 cup of whipped cream from the stand mixer. Stir until well combined.
Gently fold the sweetened condensed milk mixture back into the mixing bowl with the rest of the whipped cream.
Pour half of the mixture into the chilled loaf pan. Drizzle half of the caramel sauce over it. Then, pour the remaining mixture over the caramel and top with the rest of the caramel sauce.
Using a butter knife or skewer, carefully swirl the caramel into the mixture to create a marbled look. Do not fully mix the caramel into the mixture.
Cover the pan and freeze for at least 5 hours, or until fully set, before serving.