- Wash rhubarb. Trim ends, removing any leaves. Cut into 5cm pieces.
- Place in a non-metallic bowl. Peel onions and chop roughly.
- Place onions in a second non-metallic bowl. Sprinkle salt over rhubarb and onion.
- Cover both with warm water and leave for six hours or overnight.
- Bring undrained onion mixture to the boil in a large saucepan.
- Drain rhubarb and add to onion mixture with vinegar. Cook until rhubarb is soft.
- Stir in sugar, curry powder, mustard and pepper.
- Return to the boil. Mix cornflour and second measure of vinegar to form a paste.
- Stir into hot rhubarb mixture and let boil gently until thick.
- Spoon into hot, clean jars and seal.