Pressure cooker method: Remove the top of the can of sweetened condensed milk. Cover with aluminum foil.
Add the cooking rack to the bottom of a pressure cooker or Instant Pot. Add the prepared can. Pour water in the pressure cooker until about halfway up the side of the can.
Cover tightly, making sure the steam vent is closed.
Cook on high for 60 minutes. Allow the steam to vent naturally. Once the can has cooled, remove it from the pressure cooker.
Slow cooker method: Add the cans to a slow cooker, cover with water and cook on low for 8 hours, allow to cool naturally before opening.
Stir in the vanilla and salt, refrigerate until ready to use.