Place potato chunks in a large pot and cover with cold salted water by 1 inch. Bring to a boil, then reduce heat and simmer for 15-20 minutes until fork-tender. Drain, rinse with cool water, and let cool completely.

While potatoes cook, hard-boil the eggs (place eggs in cold water, bring to boil, cover and remove from heat for 12 minutes). Peel and cool the eggs.

In a large mixing bowl, whisk together the mayonnaise, sour cream, Dijon mustard, apple cider vinegar, smoked paprika, cayenne (if using), salt, and black pepper until smooth.

Slice the hard-boiled eggs. Quarter or chop into larger chunks. Finely slice the white parts of the green onions and add to the dressing; keep green parts for garnish.

Add the cooled potatoes and egg chunks to the bowl with the dressing. Fold gently with a spatula until everything is evenly coated.

Transfer to a serving bowl. Garnish generously with the green parts of the sliced scallions, chopped parsley, and an extra dusting of smoked paprika.

Cover and refrigerate for at least 1 hour before serving to allow flavors to meld. Best served chilled.