Place the Russet potatoes in a large pot, cover with water, and add salt until the water tastes lightly salted. Bring to a boil and cook until the potatoes are just tender. Be careful not to overcook—falling-apart potatoes will give you mushy salad. Boiling with the skins on helps keep them intact. Once cooked, let them cool slightly before rubbing off the skins.

Once cooled enough to handle, cut the potatoes into chunky cubes. Chop the hard-boiled eggs and add them to the potatoes in a large mixing bowl.

Stir in the chopped red onion, celery, and green pepper. These vegetables add crunch, color, and balance to the creaminess of the potatoes and eggs.

In a separate bowl, mix together the dark brown sugar, sweet pickle relish, mayonnaise, and mustard. The brown sugar deepens the flavor and gives a subtle sweetness that pairs beautifully with the tang of the mustard.

Pour the dressing over the potato mixture and gently fold until everything is coated. Season with additional salt and pepper to taste. Cover and refrigerate for at least an hour before serving, allowing the flavors to meld together.