Cover the potato chunks with cold water in a large saucepot. Bring to a boil and cook until the potatoes are fork-tender. Drain and return the potatoes to the pot. Add the butter, salt, pepper and nutmeg. Mash with a potato masher or electric hand mixer (essentially you are making mashed potatoes), adding warm half-and-half as needed until the potatoes are smooth and creamy. You should have a little over 6 cups of mashed potatoes.
Add the Miracle Whip, mustard, celery, onion, pickles, pickle juice, and sugar, mixing after each addition. Stir in the eggs until combined. Chill at least 1 hour or make the night before and refrigerate. Sprinkle with the chopped freshly parsley before serving.