3 1/2 cups
- In a medium saucepan simmer water, celery, onion, and caraway seeds until celery is very tender, about 30 minutes.
- Cool mixture slightly and in a blender puree in batches until smooth, transferring to a bowl.
- Stir in buttermilk and salt and pepper to taste.
- Chill soup, covered, at least until cold, about 6 hours, and up to 1 day (after that, it will lose its fresh taste).
- Before serving, season with salt and pepper, if necessary.