Mechlin cauliflower soup

Cut the vegetables and keep a few cauliflower florets separate. Stew the chopped onion in some butter and add the lettuce after a minute. Put the celery, cauliflower, stewed onion and lettuce together with sliced potatoes in a pot. Finish with vegetable stock. Season with salt and pepper. Bring to the boil and simmer for half an hour on medium heat. Put the immersion blender in the cooking pot. Now you can choose a thick soup and then you just have to stir a glass of cream through the soup and finish with a couple of steamed cauliflower florets and a few sprigs of chervil. Or you can push the soup through a sieve and only then finish with cream, cauliflower florets and chervil. In a variation on this recipe the lettuce is replaced with leeks.