Preheat the broiler on high. Line a baking sheet with aluminum foil and spray with non-stick spray. Set to the side.
While the oven pre-heats you'll make the base for the toasted marshmallow layer. Using a stand mixer fitted with a whisk attachment. Add the heavy whipping cream and condensed milk. Beat on high for one minute. While the batter mixes, spread the mini marshmallows out on the pan. Toast for about 30 seconds until golden brown but not burnt. Remove from the oven and set to the side.
Stop the mixer, remove the whisk attachment and insert the paddle attachment. Add in the toasted marshmallows. Mix on medium for 30 seconds until incorporated and not lumpy.
Pour the thick ice cream mixture into a freezer-safe container. Freeze for at least 8 hours. Scoop and enjoy once frozen.