Prepare and cut potatoes, celery, onions and dill.
In a large pot, put cut potatoes into water. Add 1 tablespoon of salt and stir. Bring water to a boil and reduce heat to medium, cook for 20 minutes (check at 15) or until desired firmness is reached.
Drain potatoes completely. Refrigerate until completely chilled throughout.
Boil the eggs: bring water to a rolling boil, spoon each egg in, turn heat off and let them sit in the water for 10-12 mins. When time is up, spoon eggs out of the water, rinse in cold water, and put into a bowl and refrigerate until chilled. When they are completely chilled, remove shells and chop.
Combine chilled potatoes, chopped celery, chopped onions, fresh chopped dill, chopped hard-boiled eggs, mayonnaise, and Dijon mustard. Add any additional salt and pepper to taste now or before serving. Garnish with extra dill sprigs. You can serve right away or chill in the refrigerator.