In a medium bowl, thoroughly combine the sweetened condensed milk, milk, vanilla, and salt. Set aside or cover and refrigerate until ready to proceed.
Pour the heavy cream into the bowl of a stand mixer fitted with the whisk attachment (or use a handheld electric mixer). Whip the cream until stiff peaks form. (This takes about 2 minutes in my stand mixer; it will take a bit more time with a handheld mixer.)
Fold the sweetened condensed milk mixture into the whipped cream. I find that a whisk will do this most effectively. You want to be careful not to totally deflate the whipped cream. That said, it will become soupier. This is okay. (To ensure I don’t over mix, I stop mixing when I still see a few pea-size pieces of whipped cream. You won’t notice them in the finished ice cream.)
Spoon the ice cream into a freezer-safe container and freeze for 6 hours. Once the ice cream has been in the freezer overnight, it’s best to let it soften for 5 to 10 minutes at room temperature (or in the fridge for about 20 minutes) prior to scooping. Homemade ice cream tends to freeze harder than store-bought varieties due to the absence of stabilizers.