Peel potatoes and grate half using the largest holes of a grater, and the rest using the smaller holes. It is a snap to do this in a food processor with the right disks. Line a bowl with a clean kitchen tea towel draped over the rim and add potatoes. Wrap the potatoes in the tea towel and squeeze out as much moisture as you can. (You may need to use a second towel—there might be more than a cup of liquid.) Discard liquid and put potatoes back in the bowl.

Add the diced onion, and sprinkle flour, salt, and baking powder (it’s optional, so don’t worry if you don’t have any) over the potatoes. Beat the eggs until blended and add to the mixture. Stir to thoroughly integrate all the elements. Let sit for 15 minutes, stirring once or twice. Chop the scallions into 1/4-inch pieces, discarding white bottoms. Add to the mixture just before cooking and stir thoroughly.

In a 12-inch nonstick frying pan, pour oil to a depth of 1 inch. Heat until oil reaches 350°. Add a heaping serving spoon of potato mixture, and press flat into the oil with back of spoon. Each latke should be about 4 inches in diameter. Cook no more than 6 at a time in the pan. The latkes will bubble vigorously. Leave them alone to cook, but after a minute or so, shake the pan gently to ensure they aren’t sticking.

When latkes are brown on the edges, about 2 minutes, turn them over using a spatula and a fork. After another minute or so, the latkes will be golden brown. Move them to a baking tray lined with paper towels to drain. Put the tray in a 200° oven to keep warm until ready to serve.