In a large soup pot, combine butter, onion, celery, and carrot. Cook until the onion begins to soften. Sprinkle with flour and cook 1 minute more.
Scrub and dice the potatoes.
Add the broth, potatoes, pickles, and dried dill to the soup. Bring to a boil and simmer, covered, over low heat for 30 minutes or until vegetables are tender.
Uncover and using a potato masher, mash to thicken to desired consistency. Stir in sour cream and simmer uncovered for 3 to 5 minutes more.
Garnish with additional sour cream, and fresh dill if desired.
