In a medium saucepan warm the olive oil, and add turnip and the leek with a big pinch of salt and sauté for 3-4 minutes.
In the meantime, peel and cut the potato to small cubes. Add to the pan, then add the stock or water & stock cube. Cook for 10-15 minutes, until all the vegetables are tender.
Mix everything with a hand blender, and mix in a bit of butter to make the soup more silky. Serve with some walnuts and a few drops of a tasty olive oil.