1. In a stockpot, heat oil over medium-high. Sauté red onion & celery 3-5 minutes, or until tender.
2. Place one can of beans into saucepan & mash slightly.
3. Add remaining beans, chicken, broth, chilies, pepper & bring to a boil.
4. Reduce heat to medium, cover & simmer soup 15 minutes.
5. In a small bowl, whisk together sour cream & flour until smooth.
6. Add mixture to soup. Cook 1-2 minutes, or until thickened, stirring throughout.