I’m not sure of the exact preparation but the two times I had them they were fucking delicious fries. I believe they soaked them and froze them like mcdonalds and then double cooked them with an air dry in the middle to get them soft inside and fluffy outside 2 or 3 day process. There was also a quite a bit of hype because of their rarity. Originally they offered them a la carte but they took them off their menu for awhile because it was so time consuming to make. Then they brought them back only to pair with >100 steak. You could ask for them sometimes and if they had extra portions they would try to accommodate your request.
Definitely worth having if you go, see this thread for more info: