Step 1

Finely chop the dark green parts of 4 large scallions for garnish. Place the remaining light green and white pieces in a medium saucepan.

Step 2

Peel 2 pounds russet potatoes. Chop half of the potatoes into 1-inch pieces. Transfer to the saucepan add enough cold water to cover by about 1 inch, and add 2 teaspoons of the kosher salt. Bring to a boil over medium-high heat. Boil until potatoes are tender, about 15 minutes. Meanwhile, prepare the remaining potatoes.

Step 3

Meanwhile, grate the remaining half of the potatoes on the large holes of a box grater. Transfer to a clean kitchen towel, gather into a bundle, and squeeze out as much liquid as possible into a large bowl. (You may need to squeeze it a few times.) Set the grated potatoes aside, still in the kitchen towel. Let the liquid in the bowl sit until the starch settles at the bottom, about 15 minutes. Separate the yolk from 1 of the large eggs (discard and save the egg white for future use) and place in a small bowl. Add the remaining egg and whisk to combine.

Step 4

When the potatoes are boiled, drain and discard the scallions. Arrange a rack in the middle of the oven and heat the oven to 400℉. Fit a wire rack inside a rimmed baking sheet.

Step 5

Drain and discard the scallions. Carefully pour off liquid in the bowl, keeping the starchy white residue at the bottom. Add the grated and boiled potatoes. Mash with a potato masher or fork until combined. Pour 1 cup buttermilk over the potatoes.

Step 6

Sift 3/4 cup all-purpose flour through a fine-mesh strainer into the bowl. Add 1 teaspoon baking powder, the beaten egg and yolk, the remaining 1 1/2 teaspoons kosher salt, and 1/2 teaspoon white or black pepper. Fold until combined.

Step 7

Heat a large nonstick skillet over medium heat. Add 1/2 tablespoon unsalted butter and swirl the pan to coat. Using a 1/4-cup measuring cup, scoop 3 to 4 portions of the batter into the skillet, spacing them evenly apart. Lightly flatten each pancake. Cook until brown and crispy on the bottom, about 4 minutes. Reduce the heat if the pancakes are darkening too quickly. Flip the pancakes, add another 1/2 tablespoon butter, and cook until the second side is brown and crispy, about 4 minutes more.

Step 8

Transfer to the prepared baking sheet and carefully wipe the skillet clean. Repeat with the remaining batter and butter. Transfer the baking sheet to the oven and bake until boxty is cooked through and warm, about 10 minutes. Serve immediately, sprinkled with the reserved scallions greens.