- In a saucepan, soften the onion and garlic in the oil. Add the milk, broth, and potato. Bring to a boil. Cover and simmer for about 20 minutes or until the potato is tender. Add the lettuce and cook for about 5 minutes.
- In a blender, purée the soup until smooth. Season with salt and pepper. Let cool. Cover and refrigerate for 4 hours or until the soup has completely chilled. Adjust the seasoning. Add chicken broth, as needed.
This soup can also be served hot.