Chop or slice the parsnips, leeks, carrots and onion.
Heat oil oil in a large pot, add the onion and garlic and fry until soft, stirring. Add the leeks and cook for a further 5 minutes, stirring occasionally.
Add the parsnips and carrots and sweat them off on a very low heat for 10 to 12 minutes. Give them a stir every so often to make sure they don't catch on the bottom of the pot.
Add the stock and bring to the boil. Simmer for 25 minutes. Add pepper. I don't add salt as I find there is enough Salt in the stock already.
Let it cool and then blitz it , either in a blender or with a hand blender.