Heat olive oil in a large pot; add shallots, leeks and nutmeg and sauté on medium heat until shallots are translucent and caramelizing, about 10 minutes.
Add spinach, parsley, mixed herbs and 2 cups broth; turn heat to low, cover and cook 3 minutes.
Transfer this mixture to a blender or food processor and puree until very smooth. Return to pot and stir in remaining broth. Bring to a boil, then reduce to a low simmer and stir in Quark or crème fraiche, salt and pepper.
Turn off heat and stir in lemon juice. Ladle into bowls and serve.