Boil the potatoes unpeeled the day before for about 10 minutes only – they should still offer clear resistance in the middle. Drain, cool completely and chill for at least 8 hours. This is what makes them firm and slightly waxy, and it is crucial for the Rösti to bind.
Peel the cold potatoes. Grate them slowly on a coarse grater, holding each potato lengthways. This is important: it makes the strands longer, so the starch binds better during frying – a tip from Swiss chef Stef Wieser. Season with the salt.
Melt 50 g of the clarified butter in the pan over medium heat, then turn it up to the highest setting. The pan must be properly hot before the potatoes go in, otherwise the Rösti will stick and soak up fat. Add the grated potatoes and shape them into a compact cake.
Fry over high heat for 3 minutes, then reduce to low and fry slowly for about 15 minutes. Do not press down or move the Rösti. It should sound crisp, almost like a whistle, when you shake the pan.
Turn the Rösti out onto a plate and slide it back into the pan. Dot the remaining clarified butter and the tablespoon of butter in small pieces around the edge and fry for another 10 minutes, until it sounds crisp again.
Slide the finished Rösti out of the pan and serve immediately while hot.
