Heat up the olive oil in a big saucepan and sauté the onion until golden-brown. Add the leeks, carrots, turnips, barley and parsnips. Cover and cook for a few minutes until starting to soften, ever so slightly.
Mix the stock in a cup with a small amount of boiling water to get all the lumps out and then add to the saucepan. Chuck in 800ml water.
Stir well, bring up to the boil then cover and simmer gently for about an hour. Check the seasoning and then serve in big bowls with lovely warm bread.