Rösti recipes spark the same fierce debate in Switzerland that chocolate chip cookie recipes do in the U.S. A flattened disc of shredded potatoes cooked in fat until crisp on the outside and tender and creamy within, rösti is served whole or in slices—and few people wish to stop at one. Who could possibly argue with—or about—that?

It comes down to technique, for the most part. Some Swiss cooks insist the potatoes must be boiled a day before cooking and left to dry out a bit in the fridge overnight. I’ve found this does...