Wash all the ingredients, peel the celery and place in a large saucepan, cut into pieces if necessary. Halve the onions, with their peel, and add them.

Add the salt, fill up with (filtered) water and bring to the boil. Simmer for about 5 minutes, then simmer for 2 hours over a low heat.

Put the stock through a sieve and bring it to the boil again, fill it into screw-top jars and turn it upside down to cool, so it stays in the fridge for a few days ... with me it never gets old :-)