Place the blueberries, sugar and salt in a medium saucepan and cook over medium heat, smashing and stirring the berries, until the mixture boils (about 5 minutes). Reduce heat and simmer, stirring occasionaly, until the berries are soft, about 5 minutes. Remove from heat and let cool slightly.
Transfer the berries to a blender or food processor and add the half and half. Puree until smooth.
Pour mixture through a strainer into a medium bowl; whisk in the sour cream (don’t worry about lumps – they’ll disappear in the ice cream maker).
Cover and refrigerate until well chilled, at least 2 hours and up to 8 hours.
Whisk the marshmallow creme into the mixture (don’t worry about lumps) and pour into an ice cream maker. Freeze according to your machine’s directions. If possible, let the ice cream harden in the freezer at least 1 hour before serving.