Peel and finely chop the onion. Set aside.
Wash, dry, and thinly slice the celery. Set aside.
Pour a few tablespoons of olive oil into a pot, add the onion and salt, stir, and gently sauté the onion for two minutes before adding the celery. Stir and cook over low flame on a small heat for 3 minutes.
Add the remaining ingredients, stir again, and cook over low heat for about 30 minutes total, or until the celery is tender.
Let cool before serving.
Store in the refrigerator for a few days.