1. In a large pot, cook potatoes, carrots, and celery in water until tender, about 20 minutes. Drain, reserving liquid. Put the vegetables back in the pot and set aside.

2. Sauté onion in a frypan in butter until softened. Stir in flour and seasonings. Add milk slowly, stirring constantly. When thick, add to cooked vegetables. Add 1 cup or more of reserved liquid until soup is desired consistency.

If heating up leftovers, more water may be added if soup is too thick.