Comments: Roestis are a traditional dish essentially Swiss.
They are either plain, or garnished with onion, bacon, sometimes also cheese.
Here I make them with onions, but it is easy to replace or complement the onions with lardons.
One of the secrets of successful roestis is fat when cooking (butter or lard), which must be in sufficient quantity. The other important point is to let the potatoes sit for 24 hours before being grated. If this is not possible, let them cool before peeling them as soon as possible. Heat the pan well, when incorporating the potatoes, it must "fry".
To flip the roestis, use a flat lid, without rim, and place it on the pan. Place the pan on a kitchen towel, hold everything firmly, and flip it in a a firm movement, without abruptness.
1 kg potatoes (Russet)
1+ large chopped onion
oil to roast
S + P
100 g lardons (opt)
The day before, cook the unpeeled potatoes in salted water (20 g/l), start cold, for ~15 minutes (not fully cooked). Take them out of the water and keep them at ambient temperature for ~24 h.
The next day, peel and grate the potatoes with a coarse grater (roestis grater - careful Microplanes are sharp! really sharp!!!).
Fry the onions (and lardons) in a little oil, and add them to the potatoes.
Season with salt and pepper and mix well by hand or with a spatula without squeezing.
If possible use a thick black iron skillet.
Put some oil in the pan, heat the pan, and put the potatoes and cook for 10 to 15 min depending on thickness. Shake from time to time, arrange the edges (tuck and thin), flatten a little, but it must remain airy.
When you start to see the edges getting golden (thinner than the middle), flip the pie using a plate (or a lid) without destroying everything (see text). Add fat (oil - butter) before sliding the pie back into the pan. Cook another 7 to 8 minutes.
During cooking, add some small knobs of butter on the edge of the pie so the melted butter flows underneath. It must not stick.