Place the Waxy Potatoes in a large pot and cover with cold water; add a pinch of Salt. Bring to a boil, then simmer until just tender when pierced with a fork, about 15–20 minutes depending on size.
Drain the potatoes and let them steam-dry for a few minutes; while still warm (but cool enough to handle), peel and slice them into rounds or bite-sized chunks and transfer to a large mixing bowl.
In a separate bowl, whisk together the Mayonnaise, Pickle Brine, Mild Mustard, Sugar, and a generous grind of Black Pepper to make a creamy, tangy dressing; taste and adjust seasoning with more Salt or Pickle Brine if you like it tangier.
Finely chop the Pickles, dice the Tart Apple (peel optional) into small cubes, and finely mince the Onion; snip the Chives into thin rings.
Gently fold the warm potatoes with most of the dressing so they absorb the flavor; add the chopped Pickles, Tart Apple, Onion and fold carefully to avoid breaking the potatoes.
Coarsely chop the Hard-Boiled Eggs and fold them into the salad, reserving a few slices to garnish if desired.
Taste and adjust seasoning with additional Salt and Black Pepper as needed. Stir in the remaining dressing if you want a creamier texture.
Cover and chill the salad for at least 1 hour to let the flavors meld. Before serving, sprinkle with the remaining Chives and arrange reserved egg slices on top for a pretty finish.
