Prep: 1. Peel and slice apples and parsnips. 2. Chop onion. Make: 1. Melt butter in a heavy pan over medium-high heat. 2. Add apples, parsnips, onion and coriander and sauté until slightly softened, about 12 minutes. 3. Add 4 cups broth and bring to boil. 4. Reduce heat to medium-low, cover and simmer until apples and parsnips are tender, about 40 minutes. 5. Then, puree soup in blender in batches, or use an immersion blender if you have one. 6. Return puree to saucepan. Thin with more broth if desired. 7. Season soup with salt and pepper. Ladle into bowls. Sprinkle with parsley; garnish with apple slices if desired and serve.
This can easily be made 1 day ahead. Just cover and chill. Then rewarm over medium heat before serving.