Saute In Butter Onions, Shallots And Proscuitto For 5 Minutes. Add Chestnuts, Salt, Celery, Fennel, And Bay Leaf. Saute 3 Minutes. Add Stock, Bring To Boil, Reduce Heat, Cover Simmer 1 1/2 Hours. Remove Bay Leaf. Allow Mixture To Cool Slightly. Process In Batches To A Puree In Food Processor. Return Puree To Pan. Bring To Boil, Add Sour Cream, Pepper Mushrooms And Parsley. Let Simmer 10 Minutes Then Serve.