Apparently, this dish originated at the famous Hasselbacken Restaurant in Stockholm.
To make them, you slice the potatoes across their width in very thin slices, leaving the skins on.
The trick is not to slice them all the way through so that the potato remains whole. (You can see why their alternative name is “accordion potatoes.”)
If you put chopsticks on either side of the potato, it will prevent you from cutting right the way through.
Once you’ve sliced your potatoes, put them (carefully!) on a lined baking sheet, paint with olive oil or melted butter and sprinkle with coarse sea salt.
Place in a pre-heated oven for an hour 200 deg C, or until they’re cooked through.
The outside should be crispy and the inside is soft and creamy.