Heat butter in 6-quart pot over medium heat. Add onion, celery and cabbage; season with salt and pepper. Stir over low heat until tender (about 7 minutes). Add potatoes, ham and chicken stock. Bring to a boil over high heat. Turn to medium heat and cook partially covered for 20 minutes.
In separate bowl, stir flour into sour cream. Slowly add 1/4 cup warm chicken stock to sour cream mixture, whisk together and pour into soup. Stir well and serve hot.