Sauté the onion, carrot, and celery in olive oil in a large saucepan until caramelized.
Add crayfish shells and stir until they turn deep red and liquid evaporates.
Deglaze with white wine and simmer for two minutes.
Add 1.5 liters of water and stock aromatics, then simmer for 40 minutes and strain.
Sauté the onion in half of the butter, then add potatoes and leeks.
Pour in the strained stock, season, and simmer uncovered for 15 minutes.
Stir in the dill leaves once the vegetables are tender.
Fry the crayfish tails in the remaining butter for two minutes and add to the soup.
Serve in bowls topped with a teaspoon of crème fraîche.