Runner bean chutney - Good Food Middle East

Ingredients

• 1.2kg runner beans
• 3 large white onions, chopped
• 700ml white wine vinegar
• 400g light brown soft sugar
• 1 tbsp ground turmeric
• 1 ½ tbsp mustard seeds
• ½ tbsp English mustard powder
• 1 tbsp nigella seeds
• 65g cornflour