The method, which comes from Chef John of Food Wishes fame and can be seen in the above video, is quite straightforward. Put the fries in a nonstick pan, making sure each one is making contact with the pan’s surface. Heat the pan over medium-high heat, and toss every 30-45 seconds, making sure the fries come back into contact with the pan after each tossing.
I tried this with some (13) fries that had been sitting in a takeout container in my fridge since Friday night. It worked well. The fries got hot, and they got crunchy—rather than crispy—on the outside. I dipped them in Russian mayo. They were good.
I still prefer the air fryer method—it’s a much more hands-off and does a better job of getting rid of that “leftover” flavor—but this is a close second. As promised, the heat from the pan drives off the moisture and gets the oil moving and grooving to the outside of the potato, which gives it the gift of crunch.
One thing to note: Chef John is serious when he says to use medium-high heat, and to keep those fries moving. Hanging out too long on any one fry facet will result in a seared, burnt fry, and that’s not what you want. (Burnt fries are still better than cold and soggy fries, but hardly ideal.)