Cook onion and celery in 1/2 cup water until barely tender. Add enough water to vegetable stock to make 2 cups. Stir some cool stock into the flour, return to pot, bring to boil and stir until thickened. saute mushrooms in butter 3 minutes. Add mushrooms, chestnuts, pimientos and chicken to celery sauce. Pour into 3-quart casserole and top with Chinese noodles and almonds Bake, uncovered at 350° 45 minutes. One and 1/2 lbs. cooked shrimp may be substituted for meat.