1Set a large saucepan over a medium heat. Add the oil and once hot, stir in the lemongrass. Fry briskly for 1 minute, then add the garlic, onions and celery and reduce the heat to low. Fry gently for 10-15 minutes.
2Add 1 litre of water and bring to the boil. Add the corn and once it returns to the boil, simmer gently for 30 minutes or until the vegetables are very soft.
3Liquidise the soup with the hand blender.
4Season to taste and stir in the creme fraiche.