In the bowl of an electric mixer, whisk together the heavy whipping cream on high speed for about 5 minutes until fluffy and stiff peaks form.
In the meantime, add marshmallows to a baking sheet lined with parchment paper and bake on 400 degrees Fahrenheit for 4 minutes.
Next fold in the sweetened condensed milk with a spatula until well incorporated. Add roasted marshmallows and continue to fold until incorporated.
Chop half of the 4oz chocolate bar into small pieces and add to the ice cream mixture, folding them in as well.
Pour into a 9x5 loaf pan and cover with foil paper and freeze for 6 hours.
To serve, remove from freezer and scoop ice cream in prepared cups, adding graham crackers, a handful of marshmallows (roasting the tops if desired) and more chocolate for garnish, if desired.