Or blackberry chutney instead of jam?
500g blackberries, 150g caster sugar, 150g red onions, 3tbsp chopped root ginger, 2 tbsp dijon mustard, 150ml white wine vinegar
Chuck everything except the vinegar into a pan over a medium heat until the blackberries burst. Season. Add vinegar then simmer with no lid on for about 15 mins. Allow to cool then spoon into sterilised jars.
Tried this last year and it was great. Could also try throwing in a bramley apple if you have any.