4 1/2 pounds baking potatoes, peeled and shredded on the large holes of a box grater
1 bunch of scallions, both white and green parts, very finely chopped
1 large egg white
1 tablespoon kosher salt
1/2 teaspoon freshly ground black pepper
3/4 cup vegetable oil
Squeeze the shredded potatoes dry. In a large bowl, using 2 forks, mix the shredded potatoes with the scallions, egg white, salt and pepper. Set two 10-inch nonstick skillets over high heat. Add 3 tablespoons of oil to each skillet. Add the potato mixture to the skillets and press into firm cakes. Set a heatproof plate or glass pie plate over each cake just to cover it. Weight down each plate with a large, heavy can and reduce the heat to moderate. Cook for 5 minutes. Uncover carefully and slide the cakes onto plates. Add 3 tablespoons of the remaining oil to each skillet. Carefully invert the potato cakes and return them to the skillets. Press the cakes firmly and cook until they are browned and crisp on the bottom, about 12 minutes longer. Slide the potato cakes onto a work surface. Cut into wedges and serve.