through the potato easily (15 minutes). Remove to a cutting board
and wait until the potato is cool enough for you to peel it with a
knife. Once peeled, slice it into ¼-inch disks. Set aside.
Coat the bottom of a nonstick skillet with olive oil and heat on
medium until adding a bit of onion makes it sizzle. Add all of the
onion, toss to coat with oil, and let the onion color a little,
seasoning with salt and pepper as it does. It should take a few
minutes to get good color.
Add the potato and let it cook directly on the heat for a few
minutes, tossing occasionally, allowing it to develop color too (it’s
sort of like making hash browns). Add the scallions and season
with more salt and pepper.
Heat a cast-iron skillet* and when it’s just warm enough to melt
cheese but not scalding hot, add half of the cheese to it in an even
layer. As it begins to melt, scoop the potato mixture on top and
press it into another even layer. Sprinkle with the other half of the
cheese.
Cook on medium-low heat, scraping around the sides, until the
cheese forms a solid crust and shaking the pan causes the whole
frico to shift.
When it detaches easily, slide the frico onto a plate, mop with a
paper towel, and invert back into the hot pan to crisp on the other
side*.
Cook until the other side is crisp (a few minutes more) and flip
back onto a plate. Serve warm with a salad on top or let it cool and
eat it later. It’ll still taste good.