Combine tomatoes, onions, sugar, vinegars, salt and mustard powder in a pan. Bring to a boil, reduce heat and simmer for 1 hour. Stir the mixture occasionally.

Add in the corn and simmer for another 20 mins

Combine the cornflour and water to form a slurry. Add to the corn mixture and bring to a boil. Reduce the heat and allow to simmer till thickened slightly.

Transfer to sterilised jars and allow to cool. Then refrigerate and enjoy!.