Cook potatoes in boiling salted water until tender. Cool slightly. Peel and
slice in thin pieces into large bowl. Add onions and next three ingredients.
Mix lightly and keep warm.
Cook bacon until crisp, drain on paper towels.
Mix vinegar, sugar and water with the cool bacon drippings, heat until
simmering. Add very slowly to beaten egg, beating constantly. Pour over
potatoes. Add bacon and parsley; mix lightly.