Richly spiced plum chutney

INGREDIENTS

• 1kg plums , halved, stoned and finely chopped
• 3 onions , finely chopped
• 100g dried cranberries or raisins, roughly chopped with an oiled knife
• 1 tbsp finely grated ginger
• 1 tbsp black mustard seeds
• 1 tbsp ground cumin
• 1 tbsp paprika
• 1 tsp chilli flakes
• 750ml red wine vinegar
• 500g light muscovado sugar