4 medium onions
250ml malt vinegar
1kg runner beans
1 heaped tbsp English mustard powder
1 heaped tbsp ground turmeric
250ml white wine vinegar
250g granulated sugar
2 heaped tbsp wholegrain mustard
2 tsp flaked sea salt
Peel and chop the onions into a small dice then tip into a large, heavy-based saucepan and pour over the malt vinegar. Bring to a gentle simmer, cover loosely and cook for 15 minutes until softened, stirring once or twice.
While the onions are cooking you can prepare the beans. Trim the ends, then cut down each side to remove any strings. Place each bean flat on the board and slice thinly lengthways on a long diagonal into seven or eight strips. How many slices you end up with will depend on the size of each bean. Ignore any that have plump little beans hiding within, as they will be the toughest.
Plunge the beans into a large pan of boiling water and return to the boil. Cook for three minutes, then drain in a colander and refresh under cold water. Drain.
Mix the mustard powder, turmeric, cornflour and four tablespoons of the white wine vinegar until smooth. When the onions are ready, stir in the sugar and remaining white wine vinegar, bring to the boil and cook for two minutes. Add the beans and simmer gently for 10 minutes, stirring occasionally. Stir the cornflour mixture until smooth once more and then pour slowly into the onions and beans, stirring vigorously to dispel any lumps, followed by the wholegrain mustard and salt.
Gently simmer the vegetables, mustard and spices for 20 minutes, stirring regularly so that the chutney does not stick to the bottom of the pan and burn. Pot the chutney into warm, sterilised jars and leave to cool. Cover, seal and store in cool dark place for at least a month.