4 large Yukon Gold potatoes, peeled
1 large egg, lightly whisked
Kosher salt and freshly ground black pepper
⅓ cup neutral oil
3 tablespoons unsalted butter
Sour cream, for serving
Applesauce, for serving
Place a large, clean kitchen towel on your counter, and place a box grater on top of it. Grate the onion on the coarse section of the grater. Remove the grater, wrap the shredded onion in the towel and squeeze over a large bowl (or your sink) to remove excess moisture. Transfer to a large bowl. If the towel is very damp, open it to a new section or get a fresh towel. Grate the potatoes on the coarse section of the grater over the towel. As you finish each potato, squeeze out the moisture as you did with the onion. Repeat until all the potatoes are grated and squeezed. Transfer to the bowl with the onion. Toss the mixture to combine. (Note: If the mixture still feels wet to the touch, dry it one more time.) Add the egg and mix to combine. Season with salt and pepper. In a large skillet, heat the oil and butter over medium-high heat. Working in batches, scoop ⅓ cup of the potato mixture into the hot oil and butter. Use a spatula to flatten slightly. Cook until golden and crisp, 3 to 5 minutes per side. Serve immediately, with sour cream and applesauce on the side.