Step 1

Place the onions into a large, heavy-based saucepan and pour over the malt vinegar.

Step 2

Bring the contents to a gentle simmer and cook for 15 minutes until the onions have softened, stirring occasionally.

Step 3

Plunge the beans into a large pan of boiling water. Let it reach a simmering point and continue to cook for another 3 minutes. Drain the beans in a colander then run it under cold water. Drain again.

Step 4

Stir in the sugar and remaining white wine vinegar into the onions, then bring it to a boil and cook for 2 minutes.

Step 5

Add the beans to the onions and simmer gently for 10 minutes, stirring occasionally.

Step 6

Mix the mustard powder, turmeric, cornflour and 45ml (3 tbsp) of the white wine vinegar until smooth.

Step 7

Pour the slurry in with the onions and beans, stirring vigorously to avoid any lumps forming.

Step 8

Stir in the the wholegrain mustard and salt.

Step 9

Gently simmer the chutney for 20 minutes, stirring regularly so that nothing sticks to the bottom of the pan.

Step 10

Transfer the chutney into sterilised jars.

Step 11

Once cooled, store in a cool dark place for at least a month.