Put the blueberries in a fairly large saucepan. Chop in a food processor or mince together the onion, unpeeled apple, garlic and sultanas. Pieces should be evenly small but not pureed. Add flavourings, sugar and vinegar, and simmer gently for 2 hours, checking flavour and adding extra chilli during this time, if desired. Bottle in small sterilised jars.