In a large bowl, whisk together heavy cream, milk, sugar, and salt until combined.
Stir in mini marshmallows until well incorporated. Cover bowl and let mixture chill in fridge for at least 4 hours, stirring on occasion.
Strain marshmallows out of mixture and pour strained milk/cream mixture into ice cream maker. Process according to manufacturer's directions, likely running for about 20 minutes.
When ice cream is almost done processing, spoon marshmallow fluff into mixture and let it swirl in.
Transfer ice cream to containers and freeze for at least 4 hours before serving.