Jerusalem artichoke soup

1) Heat the oil in a large pan and fry the onion until soft and translucent.
2) Add the artichokes and fry for 3-4 minutes more.
3) Pour in the stock and cream and cook over a medium heat until the vegetables are soft.
4) Add the lemon juice and cook for five more minutes.
5) Pour the mixture into a food processor or use a hand blender and blitz until smooth. Season to taste.
6) Serve topped with croutons and a swirl of olive oil.