Place onions into Thermomix bowl and chop 3 sec/sp 5.

Add tomatoes amd mix with spatual. Chop 3 sec/sp 5. Repeat for 1 to 2 more seconds if necessary.

Place into a large container and sprinkle with the salt.

Refrigerate overnight.

Next day, drain well and place into a large pan with the sugar. Pour over enough vinegar to cover and bring to the boil. Boil together for 5 minutes, stirring regularly.

Mix the curry powder and mustard to a paste with a little extra vinegar and add.

Simmer gently for around 2 hours, stirring regularly to ensure it doesn't catch on the bottom of the pan.

Thicken with cornflour paste - around 2 -3 Tbsp of cornflour. Place into sterlised jars and seal tightly. Turn jars upside down for 30 minutes. When turned upright, lids should pop down.