Cut up the potatoes and boil them. When they've got about five minutes left, stick the eggs in the pot as well. They should be hard-boiled.
Mix the mustard with the mayo and set it aside.
When the potatoes and eggs are done, mash five of the potatoes and add the mayo mixture. Cut the other three potatoes into small pieces and add as well. Remove boiled eggs from shells and cut into slices. Add to salad.
Chop the celery and apple into bite-sized pieces and add, with peas, to salad. Stir it all together, sprinkle paprika on top, and enjoy!