Peel and cube the Russet potatoes into uniform 1-inch pieces. Place in a large saucepan, cover with cold water, and add a pinch of salt. Bring to a boil, then reduce to a simmer and cook for 7-8 minutes until tender but firm. Drain and cool.

Finely chop the celery and onion, and dice the hard-boiled eggs. In a large mixing bowl, combine the cooled potatoes with chopped celery, onion, salt, and black pepper, tossing gently to mix.

In a separate bowl, whisk together the mayonnaise, mustard, vinegar, and sweet pickle relish until smooth. Adjust seasoning with salt and pepper.

Pour the dressing over the potato mixture and stir gently to coat, ensuring potatoes remain intact.

Cover tightly and refrigerate for at least 30 minutes to allow flavors to meld. Serve chilled, garnished with chopped green onions if desired.