Boil potatoes until fork tender. Drain, allow to cool and when cool enough to handle, cut into cubes.
Slice onions into quarters and then into thin slice. Add onions, celery, apples, olives and pickle to potatoes.
Stir together mayonnaise, vinegar, mustard and steak sauce. Pour over potatoes and combine gently so as not to break up the potatoes. Season with salt and pepper to taste.
Cover and refrigerate for several hours or overnight.