Coarsely grate the potato and onion using a box grater or food processor. Pop a clean tea towel into a large mixing bowl, scoop the potato mix into the tea towel and season with the salt flakes. Squeeze the salt into the mix with your fingers.
Twist the towel up into a swag, then squeeze with all your might to let the liquid drip out into the bowl below. I like to use a wooden spoon to act as a tourniquet, but you’re welcome to just use brute force. It’s quite the workout! Don’t throw out the liquid just yet!
Transfer the potato mix into a fresh bowl, then after 10 minutes, pour off the liquid in the bowl, leaving the gluey starch at the bottom of the bowl. Transfer this starch to the potato mix and reincorporate with your hands.
Heat a 28cm heavy-bottomed pan on medium heat, and add a quarter of your oil into the bottom of the pan (it’s roughly 2-3 tbsp, depending on your tablespoon of choice!).
Sprinkle in half of your potato mix loosely. Set the timer for 15 minutes, then walk away to live your life, get your garnishes together, maybe make a salad.
After 15 minutes, come back and scoop in the sides. Use a chopping board or large flat plate that fits just inside the pan, shake the pan gently to loosen the rösti, then pop the plate on top and flip with confidence (careful of leaky oil… but you should be right!)
Pour another quarter of the oil into the bottom of the pan and carefully usher the rösti back in on the other side with a few choice words and a spatula. Set the timer for another 10 minutes. Go set the table, have a sip of water.
Slip the finished rösti onto a serving platter or chopping board and load up with your chosen accoutrements (see top tips).
Before you head to the table, pop half of the remaining oil into the pan, sprinkle in the rest of your potato mix, set the timer for 15 minutes and away you go! By the time the first rösti is well on its way to being devoured, your second should be coming up for a flip. Repeat steps 6-8.