1 very large Russet potato (1 pound or two medium), scrubbed
1 small onion
1 large egg
¼ tablespoon kosher salt
¼ teaspoon freshly ground black pepper
½ cup vegetable oil
Sour cream, ikura (salmon roe, optional), and chopped chives, for serving
Fill a large bowl with cold water. Using the large holes on the side of a box grater, grate the potato and onion, transfer them to the water, and let them sit for 5 minutes.
Place a clean kitchen towel on the counter near the sink. Pull the potatoes and onions out of the water, squeeze out as much water as you can back into the bowl, and let the water settle. Dump the potatoes and onions onto the towel, fold the towel over the mixture, and squeeze out and discard as much of the liquid as you can from the potatoes and onions. Gently drain the water out of the large bowl, tipping out all the water but leaving the white potato starch at the bottom.
Add the squeezed potatoes and onions to the sludge in the bowl (mmm, sludge), then add the egg, salt, and pepper and stir it all together.
Meanwhile, heat ¼ cup of the vegetable oil in a 10-inch skillet over medium heat (not high - don’t worry, they’ll still crisp, but without burning). By the tablespoon, spoon the potato mixture into the pan, pressing down gently, and fry until each side is golden and crisp, 2 minutes per side.
Transfer to a paper towel-lined plate or baking sheet to drain. Repeat with the remaining batter and oil. Top with sour cream, ikura (if using), and chives and serve immediately. Serve fresh, or keep warm in a low oven, uncovered on an oven-safe plate, until ready to serve