1. Peel and cut 2 lbs. sweet potatoes into 3/4-in. chunks. Bring a large pot of salted water to a boil. Add potatoes and 2 whole eggs. Reduce the heat to maintain a steady low boil and simmer for 12 minutes. Transfer eggs to a bowl of ice water. Potatoes should be just tender; if not, cook until a thin-bladed knife slides through easily. Drain potatoes well and rinse with cold water. Peel and halve eggs. In a very large bowl, whisk together 1/4 cup mayonnaise, 1/4 cup sour cream, and 1/4 cup sweet relish. Add potatoes and 3 stalks thinly sliced celery. Gently fold until evenly coated. Season with kosher salt and pepper. Garnish with eggs and parsley, if desired. Serve immediately or refrigerate for up to 1 day.