Cut the potatoes in half and put them in a large pot. Cover with cold water and add the kosher salt. Bring to a boil, then reduce the heat to a simmer. Simmer until the potatoes are fork-tender, about 20-25 minutes. Drain and rinse under cold water.
Once the potatoes are cool, cut them into bite sized chunks and put in a large bowl.
In a small bowl, whisk together the mayonnaise, sour cream, mustards, paprika and dill. Stir in the celery, onion and pickles.
Use a rubber spatula to gently stir this mixture into the potatoes until they are all well coated. Season with salt and pepper and stir again. Allow to chill in the fridge for at least 2 hours before serving.