How to Make It
In a large saucepan, heat the oil over moderately low heat. Add the onion, fennel, celery, and 1/4 teaspoon of the salt. Cook, stirring occasionally, until the vegetables start to soften, about 10 minutes.
Add the potatoes, broth, water, the remaining 1 1/4 teaspoons salt, and the pepper. Bring to a boil. Reduce the heat and simmer for 5 minutes. Stir in the pasta and simmer for 5 minutes longer.
Add the Swiss chard and spinach and bring the soup back to a simmer. Cook, stirring occasionally, until the greens are wilted and the pasta is tender, about 5 minutes longer. Stir in the Parmesan.
You'll need a total of eight cups of shredded greens for this soup. Use one or any combination of the following: Swiss chard, spinach, escarole, green cabbage, or kale. The more variety the better.