Clean the spring onions, wash and cut into fine rings. Wash the celery stalks, remove hard strings and cut into thin slices.
Briefly fry the vegetables in butter, dust with flour and sauté briefly, deglaze with the broth, the Prosecco and the milk while stirring and cook over medium heat for about 10 minutes.
Puree everything with a hand-held blender, add creme fraiche and the chopped Saint Agur. Mix the soup again well with the blender. Season with salt and pepper to taste.
Wash chives and cut into fine rings. Serve the soup into 4 soup bowls and sprinkle with the chives. Goes well with toasted baguette slices rubbed with garlic.