Warm potatoes seasoned at every stage, mustard for the tang, relish for the sweetness, and the mayonnaise last. Mixed by hand, and better on the second day.
Better the second day
Cover and refrigerate until properly cold before serving — it is at its best the day after, and keeps for a week.
Cut the peeled potatoes into even pieces and cover them with water by two inches in a large pot over high heat. Bring to the boil, then turn down to a steady simmer. Cook until a knife pierces the centre without much resistance — soft enough to mash, but not falling apart. How long depends entirely on how big you cut them.
Drain and transfer to a large bowl. Let them cool until you can handle them with your hands, and no further — everything from here is done warm.
Elbows in. This is a hand recipe; a spoon does not mix it the same way.
Season the potatoes with the seasoning salt and the pepper, tasting as you go. Then take a masher to them — but not to all of them. Leave some pieces whole so the texture varies. They should already taste good on the seasoning alone, before anything else goes in.
Add the mustard a little at a time, tasting for the tartness you want. Stop where you like it.
Add the diced celery, the sliced green onions and the chopped eggs, and mix them through by hand. Keep the halved eggs back for the top.
Add the relish gradually, tasting as you go. This is the thing that decides whether you end up with a wet potato salad or a dry one, so it is worth taking slowly.
Too much relish and there is no coming back. Add less than you think, then taste.
Add the mayonnaise and mix it thoroughly, all the way to the bottom of the bowl.
Lay the halved eggs over the top, dust with sweet paprika and scatter the parsley. Cover and refrigerate until it is properly cold before serving.