Thaw the lima beans and place in the bowl of a food processor or blender.
Add the margarine, scallions, curry powder, salt and pepper, tarragon, and parsley. Process until smooth.
Place the lima bean mixture into a pot. Pour the broth and milk. Bring to a simmer, cover and simmer for 10 minutes. If the soup is too thick add water to bring it the consistency of a thick cream soup.