Brown pieces in hot butter in heavy frying pan, then remove chicken to casserole.
Reheat butter in pan and add flour, blending carefully. Heat and stir until mixture is light brown. Cool roux thoroughly. Will not curdle if roux is cooled before sour cream is added.
Add sour cream slowly, mix well and simmer for a few minutes. Pour this over chicken in casserole. Add mushrooms, seasonings, parsley and scallions (green tops and all) and water. Sprinkle paprika over mixture.
Cover tightly, place in a 325 degree oven and cook for 1 1/2 hours, or until chicken is tender.
The sauce that is made is VERY thin, so I would make a larger roux, or at the end add a thickener.