Peel the onion and finely chop. Rinse the asparagus, peel the bottom third and trim the ends. Cut the asparagus into small pieces.
Heat butter in a large saucepan and saute the onion until soft. Add the asparagus pieces and fry over low heat for 10 minutes. Pour in the vegetable broth and simmer covered for 15 minutes.
Puree the asparagus soup with immersion blender, stir in the cream and simmer covered for about 10 minutes. Stir in the white wine, and season with salt, pepper and nutmeg.
Serve the soup in bowl garnished with asparagus slices.