Preheat oven to 350. Add 1 tablespoon butter and olive oil to a medium skillet. Add onion and celery and saute for 5 minutes. Place chicken in a buttered 9x13 pan. Top with broccoli, onion, celery, and water chestnuts. In a large bowl combine soups, broth, and sour cream. Add seasonings. Pour over veggies. Place Ritz crackers in a plastic baggie, and crush. Place in a small bowl and add melted butter, stirring until combined. Sprinkle mixture on top of casserole. Bake in the oven for 35-40 minutes, or until topping is golden brown. Serve over buttered noodles or rice.