On a lined cookie sheet, toast the marshmallows under a hot broiler until they are golden.
Let cool.
Whip the cream until stiff peaks form.
Add the sweetened condensed milk and dash of salt to a medium mixing bowl.
Fold in the whipped cream.
Add the chopped chocolate, half of the toasted marshmallows, and 3 graham crackers (broken into pieces) to the whipped cream mixture.
In a freezer-safe container (I used a 9x5 bread pan), pour half of the mixture.
Spread evenly in the container, then add half of the remaining marshmallows, and pieces from half of the remaining cracker.
Drizzle with slightly warmed hot fudge (only warm it enough to get it to a drizzling consistency, it should not be hot).
Spread the remaining half of the whipped cream mixture into the pan.
Add the remaining marshmallows, remaining graham cracker (broken into pieces), and drizzle with more of the warmed hot fudge.
Cover well and freeze for at least 6 hours.