Fry the onion in a saucepan lightly in a mixture of butter and olive oil.
Dice the celery root.
Also cut the pumpkin into cubes.
Send the celery and pumpkin to the frying pan with the onion and fry a little.
Pour in the milk, cover and simmer for 30-35 minutes on low heat, adding salt to taste.
Meanwhile, marinate the chicken fillet in 1 tablespoon of olive oil with the addition of white wine vinegar, a mixture of Provencal herbs and salt for 10 minutes.
And fry in a hot frying pan or grill on both sides. Keep warm until serving.
Grind the finished soup with a blender into a puree, add milk and salt. Return the soup to the pot and reheat.