American
Coarsely grate the peeled potatoes, put the shreds in a bowl of cold water and swirl for 1 minute to rinse off the surface starch.
Drain the potatoes, wrap them in a clean kitchen towel and twist it hard to squeeze out as much liquid as possible.
Toss the dry shreds with the salt and pepper.
Heat the oil and half of the butter in a large nonstick or cast-iron frying pan over medium-high heat until the butter foams.
Spread the potatoes in an even layer about 1.5 cm thick, press them down with a spatula and cook without stirring for 8-10 minutes, until deep golden underneath.
Cut the cake into 4 wedges, flip each one, add the remaining butter around the edges and cook for 6-8 minutes more, until the second side is crisp and brown.
Sprinkle with the chives and serve hot.