Place the potato chunks in a large pot and cover with cold water by about an inch. Add 1 tablespoon of kosher salt to the water.
Bring the pot to a boil over high heat, then reduce to a simmer. Cook for 12-15 minutes, or until the potatoes are fork-tender but not falling apart.
Drain the potatoes in a colander and spread them out on a baking sheet to cool completely. This helps them firm up and prevents mushiness.
While the potatoes cool, make the dressing. In a medium bowl, whisk together the mayonnaise, sour cream, Dijon mustard, apple cider vinegar, garlic powder, and black pepper until smooth.
In a large mixing bowl, combine the cooled potatoes, celery, green onions, dill, and chopped eggs (if using).
Pour the dressing over the potato mixture and gently fold everything together until evenly coated. Be careful not to overmix to keep the potatoes intact.
Cover the bowl and refrigerate for at least 2 hours, or ideally overnight, to let the flavors meld. Give it a gentle stir before serving.