Boil a large pot of water. Add potatoes. Cook until tender, 15 minutes. Scoop out and transfer to large plate. Refrigerate until cool, 40 min. Add eggs to same water. Cook for 9 minutes. Scoop out and transfer to a bowl of cold water (this aids in separating the shell from the egg). 5 minutes and peel and slice. Set aside. Peel and chop remaining eggs and quarter potatoes. Whisk mayo with sour cream, lemon juice, curry powder and salt in a large bowl. Add potatoes, chopped eggs, gherkins, apple, red onion and dill. Toss until coated. Transfer to a platter. Top with reserved eggs and more sliced gherkins and dill.