I picked up a bunch of watercress somewhere with the plan to make watercress soup. When I lived in France I ate a lot of watercress soup. It's made with potatos to it is a thick soup with a nice peppery kick from the cress. I didn't know what watercress actually is so I looked it up on Wikipedia and found an interesting article. It is related to mustard and is a member of the cabbage family.
4 peeled and sliced potatoes
3 to 4 leeks peeled of the outer leaves and sliced (white part and tender green part)
1 T (yes, a tablespoon) salt
3 T butter
2 quarts of water (or stock or a mixture of stock and water)
A large handful of watercress
Put the water in a large pot. Add potatoes and leeks and salt. Simmer for 45 minutes. Add the cress. Simmer for 5 minutes. Puree the soup in a blender or food processor being careful not to burn yourself like I did. If you are using a blender, put a kitchen towel over the lid and hold it firmly. Pour soup back into pan. Add butter and stir until it melts. Season with black pepper and more salt if necessary.
Makes enough for a small army.