1. | Cook potatoes until tender. Cool. Peel if desired, then dice. Place in bowl. |
2. | Cut onion into quarters and slice thin; add to potatoes along with apple, celery and pickle relish. |
3. | In a small bowl, stir together the mayo, mustard, vinegar, and Worcestershire sauce. Spoon over potatoes and gently mix together. |
4. | Season with salt and pepper. |
5. | Cover and chill for at least two hours or overnight. |