Cut the root off the onion, this makes it easier to peel off the skin. Cut the onion in half and put it in the sauce pan.
Scrub the carrots and cut off the tops. Cut each carrot in half and put it in the saucepan.
Wash the celery and cut it in half and add it to the pan with the other ingredients.
Add enough water to cover the vegetables and bring the pan to the boil. Lower the heat and simmer the vegetables for 25-30 minutes.
Allow the stock to cool completely and strain the stock through a sieve to remove the vegetables.