Clean and wash the spring onions. Cut the whites into rings. Put the (beautiful) green aside. Peel and roughly grate potatoes, carrots and celeriac, e.g. in a food processor.
Heat the butter in the soup pot and sauté the onion rings in it. Add the grated vegetables and sauté a little over low heat.
Rinse the celery, cut into slices and add. Pour in the vegetable stock and simmer for 15 minutes. In the meantime, cut the green of the spring onions into very fine rings.
Add the crème double, puree everything finely and cook for another 5 minutes in an open saucepan until the consistency is nice and creamy. Be careful that the soup does not stick.
Slightly season the soup with salt, pepper, nutmeg and lemon juice.
Mix the green onion rings and the crabs into the soup, except for a tablespoon each, and heat briefly. Spread on plates or soup bowls and sprinkle with the remaining shrimp and spring onion rings.
Tip:
At parties, I serve the prawns separately from the soup, as not everyone likes them.
Narrow strips of cooked ham are well suited as an alternative insert.
With four times the amount you get a 9-liter pot full. Warm up again carefully and stir often, as the soup sets up quickly.