Add potatoes and onions to the boiling water.
Cover, and cook for about 14 to 20 minutes, or until potatoes are tender.
Mash the potatoes slightly with a fork to thicken the soup a little, if desired.
Add milk, margarine and seasoning. Heat to serving temperature.
Top each serving with a dab of sour cream and sprinkle with finely cut parsley.
Yield: 4 serving, a cup each.