Place the grated potatoes in a clean kitchen towel and squeeze out as much excess moisture as possible. This step is crucial for achieving crispiness.

In a large bowl, combine the grated potatoes, salt, black pepper, flour, and beaten egg. Mix until well combined.

Heat 2 tablespoons of vegetable oil in a large skillet over medium-high heat. Once the oil is hot, add half of the potato mixture, pressing it down with a spatula to form a flat cake.

Cook for about 5-7 minutes until the bottom is golden brown and crispy. Carefully flip the rosti using a large plate or spatula, adding the remaining oil if needed.

Cook the other side for another 5-7 minutes until golden brown and crispy. Remove from the skillet and drain on paper towels.

Repeat with the remaining potato mixture, adding more oil as necessary.

Serve hot with sour cream or applesauce, if desired.