1Place the potatoes in a large pot and add enough cold water to cover them. Cover the pot with a lid and bring to a boil. Cook until the potatoes are just this side of done, about 15 minutes.
2Drain and let cool until you can handle them. When cool, cut the potatoes into quarters or halves, depending on the size of the potatoes.
3In a large bowl, toss together the potatoes, celery and parsley. In a small bowl, stir together the sour cream, garlic, lemon zest, lemon juice, dill pickle relish, tarragon, salt and black pepper. Pour the dressing over the potatoes and toss to coat. Cover and refrigerate for several hours or overnight.
Taste test and adjust seasoning right before serving.