Put potatoes in a large pot of salted
water; bring to a boil. Cook until just tender,
20 to 25 minutes. Drain; let cool.
Stir together mayonnaise, lemon juice,
mustard, and dill; season with salt and
pepper. Peel potatoes; cut into 1-inch
chunks. Fold into mayonnaise mixture.
Fold in celery, onion, scallions, and eggs
(reserving some scallions for garnish).
Refrigerate, covered, until ready to serve.