In a stockpot, gently saute the onion and leek in the olive oil for 10 minutes or until soft.
Add the chopped vegetables and pour in enough vegetable stock to come to 1 cm below the top.
Bring to the boil, cover and simmer for 30 minutes or until all the vegetables are soft.
Allow to cool slighly then puree in a blender (for a really smooth soup) or with a stick blender. Season to taste.
