Creamy Green Beans

1/2 cup thinly sliced onions
2 tablespoons butter or margarine
4 ounce can mushrooms
Boiling water
1 pound fresh green beans cut into 1 inch pieces or 20 ounces frozen
green beans
1 teaspoon salt
1 cup sour cream

Fry onions in butter over low heat in a heavy saucepan, stirring
occasionally, until onions are golden. Drain mushrooms, saving
liquid, and add to onions; cook and stir until mushrooms are hot. Add
enough water to mushroom juice to equal 2/3 cup liquid and add to
onions and mushrooms. Add beans and salt; cover and cook about 15
minutes or until beans are tender-crisp. Drain off any liquid. Add
sour cream; heat to serving temperature but do not let boil after
cream is added. Serve hot.