Bring potatoes to a boil in the broth and water; turn down to simmer. Sauté leeks and garlic in a little oil. When potatoes are about half done, add leeks and garlic, carrots, greens, and seasonings. Simmer until potatoes are tender. Bring to a slow boil. Mix flour with a little water and gradually add to soup until desired thickness is reached. Remove from heat. Add milk or cream if desired.