Place 1 cup of water, potatoes and eggs into the bottom of the instant pot.
Close the lid and make sure the pressure release is closed.
Set the instant pot to manual, high pressure for 4 minutes.
Quick release the pressure and immediately drain the potatoes and eggs and rinse them under cold water until they are no longer steaming.
Place the eggs into an ice water bath.
Add potatoes to a bowl and mix together with onion, celery, mayonnaise, mustard, salt and pepper.
Slice two eggs crisscross as shown, and mix with the potatoes.
Place potato salad into a serving bowl and top with 1 sliced egg.
Refrigerate until ready to serve.