To prepare Finely dice the onion and the peeled garlic. Peel and dice the potato and turnip. Coarsely chop the leek. Peel and chop the carrot into slices. Chop the celery and courgette. Coarsely chop the tomato and the chervil.
In a large saucepan and over medium heat, soften the onion, garlic and potato in the butter for 3 minutes – this will extract maximum flavour but stir to prevent browning. Season with salt and white pepper.
Add the turnip, leek, carrot, celery, courgette and tomato. Stir and add the boiling water. Bring to the boil, increase the heat, and cook on a fast boil for 5–7 minutes, until the vegetables are just tender. Stir in the chervil.
To finish the soup, stir in the crème fraîche or butter (or both, if you wish). Taste and correct the seasoning if necessary, then serve. This soup can be puréed in a blender if you prefer a smooth texture.