Melt butter in large soup pot. Add leeks and onion. Slowly saute until soft but not browned. Add potatoes and stock. Add salt and marjoram.

Bring to boil. Boil slowly 30 minutes. Reduce heat to a simmer, add half-and-half and simmer 10 minutes, stirring constantly. Add heavy cream and white pepper just before serving. Makes about 12 servings, 1 cup each.