ATK: Lentils du Puy, sometimes called French green lentils, are ATK’s first choice for this recipe, but brown, black or regular green lentils work, also. Cooking times will vary depending on the type of lentils used. It’s important to note that lentils lose flavor with age (something that has never occurred to me) so it’s wise to select from your freshest source. The soup can be made in advance. After adding the vinegar in step 2, cool the soup to room temperature and refrigerate it in an airtight container for up to 2 days. To serve, heat it over medium-low until hot, then stir in the parsley.