bring a large pot of salted water to a boil over high. while the water comes to a boil, prepare your dressing: in a large bowl, stir together pickles, celery, scallions, mayonnaise, buttermilk, parsley, dill, capers and brine, mustard, lemon zest and juice, and sugar. season with 2 teaspoons salt and 1 teaspoon pepper.