Bring a pot of salted water or broth to a boil. Add potatoes and boil for 10 minutes or until fork-tender. Drain the potatoes and set aside to cool.
Cut bacon into small pieces and place in a large skillet over medium-high heat. Add onion and cook until bacon becomes crispy and onions are cooked through. Using a metal slotted spoon or spatula, remove the bacon from the pan and set on a plate lined with a paper towel. Remove all but about 1/3 cup of bacon grease from the pan.
Combine apple cider vinegar, dijon, sugar, salt and pepper in a bowl. Pour vinegar mixture into the pan with the bacon grease and stir well, scraping the bottom of the skillet to deglaze the pan. Remove from heat and set aside. Cut potatoes in half and place in a large bowl. Pour the bacon-vinegar mixture over the top and add the bacon. Gently stir with a rubber spatular to combine.
Garnish with parsley and serve hot or refrigerate to serve later.