Brush the celery bulb under running water. Bring 1250 ml of water with the salt and vinegar to the boil, add the celery tuber and cook for approx. 1 - 2 hours until soft. Then remove, peel and cut into small pieces.
Whisk the oil with the vinegar and canned milk, add the onion and season with salt and pepper. Put in the celery pieces, mix and season again if necessary.