Add the onions, celery, tomatoes and apples to a preserving pan. Pour in the measurement water and vinegar, then bring to the boil. Reduce the heat, cover and simmer gently for 1 hour, stirring and mashing from time to time with a fork, until the tomatoes and apples are pulpy.
Allow to cool slightly, pour into a scalded jelly bag suspended over a large bowl and allow to drip for several hours.
Measure the clear liquid and then pour back into the rinsed preserving pan. Weigh 500 g (1 lb) sugar for every 600 ml (1 pint) of liquid, then pour into the preserving pan. Add the tomato purée and lemon juice and heat gently, stirring from time to time, until the sugar has dissolved.
Bring to the boil, then boil rapidly until setting point is reached (20–30 minutes).
Skim with a draining spoon or stir in butter if needed. Stir in the sun-blush tomatoes and vodka, if liked, and leave to stand for 15 minutes so that the tomatoes don't rise in the jelly when potted. Ladle into warm, dry jars, filling to the very top. Cover with screw-top lids, or with waxed discs and cellophane tops secured with elastic bands. Label and leave to cool.
To serve, this jelly goes well with cold meats, such as salami and parma ham, olives and sunblush tomatoes.