Scrub the potatoes under running water with a soft brush.
Quarter them and drop them into a kettle of cold, salted water.
Bring to a boil and cook until tender but still firm, 8 to 10 minutes after the water reaches a boil.
Meanwhile, chop the bacon and saute in a small skillet until crisp.
Remove bacon and reserve.
In the bacon fat remaining in the skillet, saute chopped shallots until tender but not at all browned, 5 minutes or so.
Reserve shallots and fat.
When the potatoes are done, drain them and drop them into a mixing bowl.
Pour vinegar, olive oil, shallots and reserved bacon fat over the still-hot potatoes.
Season with salt and pepper to taste, and gently toss.
Add purple onion and parsley and toss again.
Cool to room temperature, cover, and refrigerate.