Instructions

  1. In a large saucepan cook the onion, celery, and carrot in butter over medium-low heat, stirring, until the vegetables are tender.
  2. Stir in the broth and rosemary, and bring to boiling.
  3. Whisk in the potatoes, a little at a time, bring the soup to a boil again, stirring, and add the vinegar, parsley, and season with salt and pepper to taste.