Dice the celery into small pieces about ¼" in size. Slice or chop the sweet pickles. Measure out the liquid ingredients. Don't chop your potatoes yet, you want to do that just before you cook them so they don't turn brown. You also don't want to soak them in water because the starch is what helps the dressing stick on the potatoes and soaking the potatoes removes some starch.
Whisk the cornstarch into the milk. Turn the Ninja Foodi on high sear/sauté and add the milk and cornstarch mixture and add to the inner pot.
Add mustard, brown sugar, salt, onion powder, and garlic powder and whisk to combine. Bring to a boil while whisking constantly.
Turn the Ninja Foodi off. Lightly whisk the egg in a bowl and pour about 1 tsp of the dressing into the egg and whisk. This is called tempering your egg and will bring the egg closer to the temperature of the dressing. With the Foodi turned off, slowly whisk in the egg. Stir constantly. The egg will combine with the dressing, but should not cook. If you see the egg starting to cook, stop adding it and let the pot cool down just a little more. The temp of the sauce should reach 135°F/57°C and be thickened. Remove from the pot (unless you have two pots) and reserve for use later. Clean the pot.
Cut the potatoes into bite size chunks about 1-1½" and add them to a clean, dry inner pot. Don't add any liquid until just before you are ready to go under pressure or the starch from the potatoes can leach out into the water and make it more difficult to go under pressure.
Add in ½ cup water, salt, vinegar, and ¼ cup of sweet pickle juice. Add the eggs on top and put the pressure lid on. Turn the valve to seal and set the pressure on high for 1 minute. When the time is up, allow the pot to naturally release the pressure for 5 minutes and then manually release the remaining pressure. You should only have a slight amount (a couple tsp at most) of liquid left. If you have more liquid, you will need to drain that out.
Remove the eggs and place them in an ice bath.
While the potatoes are hot, add the cooked dressing, the mayonnaise, celery, and sliced sweet pickles and stir well. Adjust seasonings if needed. Peel and chop the eggs. Add them to the potato salad and stir to combine. Chill for at least 4 hours.
Serve and enjoy!