Season chicken filets with salt and pepper, bring soup to a boil. add the filets and simmer about 25 minutes. Clean and peel celery and cut into equal pieces. Heat butter an sauté celery in a saucepan until al dente and season with salt.
For the sauce, chop the shallot finely and sauté them in butter, dust with flour and stir well. Pour in chicken broth and white wine and beat with a whisk.
Fold in creme fraiche and cream and season to taste with salt and pepper.