In a large saucepan cook onion or leek in hot margarine or butter until tender but not brown. Stir in the undrained oysters and salt. Cook over medium heat about 5 minutes or until oysters curl around the edges, stirring occasionally.
Stir in the milk, half-and-half or light cream, parsley, pimiento (if desired), and white pepper. Heat through. If desired, top each serving with margarine or butter. Makes 12 appetizer servings.