In a large pot over medium-high heat, boil potatoes (with skins on) just until barely done or tender when pierced with a fork; drain and cool slightly.
As soon as you can handle the potatoes, peel and cut into chunks; place into a large bowl.
Cut onion into quarters and slice thin; add to potatoes along with apple, celery, green olives, and sweet pickles.
In a small bowl, combine mayonnaise, Dijon mustard, cider vinegar, and steak sauce or soy sauce. Spoon over potato mixture; mix gently. Season with salt and pepper.
Cover and refrigerate at least 2 hours or overnight before serving.
* Look for sweet onions that are light golden-brown in color, with a shiny tissue-thin skin and firm, tight, dry necks. When cut into, sweet onions should have a creamy white interior. Avoid onions that have soft spots or surface bruises. Avoid onions that are soft or sprouting.
Young onions are sweeter than old ones. They should have absolutely NO SMELL whatever. If they do, they are probably bruised somewhere under the skin and are on their way out.
Sweet Onion Potato Salad Recipe: https://whatscookingamerica.net/salad/potatosal.htm