Loved by all, this homemade ketchup is less sweet than many commercial products. It is very simple to make and a useful way to use up a bumper crop of tomatoes each year.
Sterilize enough bottles in the oven so that they are ready to use. If using screw-top bottles with metal lids, fit with cut-out card discs to prevent the ketchup coming in contact with the metal.
Heat the oil in a large, heavy-based saucepan. Add the onions and fry gently for 10–15 minutes, stirring occasionally, until softe