Ensure all potatoes are approximately the same size. Fill a large pot with plenty of water and boil the potatoes with their skins on for about 10–15 minutes. To check doneness, insert a knife into a potato's center; it should still be slightly firm. Then, drain the water.
While the potatoes are cooking, finely chop the onion. Heat the broth with the raw onions, vinegar, salt, and pepper on the stove. It should be hot but not boiling.
Once the potatoes are cooked, peel and thinly slice them using a grater. Alternatively, you can use a small knife, but try to make the slices as uniform as possible.
Pour the seasoned broth over the still-warm potato slices and gently mix everything. Cover and let the potatoes marinate for a maximum of 30 minutes, preferably only 20 minutes.
Now it's time to fine-tune the potato salad: Add the oil and check the consistency. It should be nicely creamy and a bit mushy. If the potatoes have absorbed too much liquid, add a splash of mineral water or broth. Optionally, add a bit of nutmeg and adjust the final seasoning with salt. Gently fold everything together.
Finely chop the chives. Your warm potato salad is now ready to be served.Portion out onto plates and sprinkle a handful of chives over each serving.