Peel, quarter, and core the fruit. In a food processor, blitz (in batches if necessary), then transfer to the slow cooker.
Stir in sugar, salt, and the cinnamon stick.
Cover and cook on high, 4 hours.
Remove the cinnamon stick and reserve.
Transfer the mixture to a food processor (in batches if necessary) and blitz until smooth.
Return to the slow cooker, along with the cinnamon stick, and cook on high uncovered, until mixture is thick and browned, 4 hours.
Discard cinnamon stick and let the mixture cool.
Transfer to airtight containers and refrigerate.