2 1/2 pounds Idaho, russet or baking potatoes (about 4 large), scrubbed
1 large onion, peeled and quartered
2 large eggs, separated
3 tablespoons matzoh meal or bread crumbs
1 to 2 teaspoons kosher salt
1 teaspoon black pepper
Corn or canola, or vegetable oil for frying
Line a large baking sheet with two layers of paper towels; set aside.
Using the coarse holes on a hand-held box grater or the medium-coarse shredding disk of a food processor, shred the potatoes and onion together. Transfer potato-onion mixture to a large colander set over a bowl.
Over the colander, use your hands and squeeze the potato mixture, squeezing out as much liquid as possible. After you finish squeezing, let the mixture stand in the colander for 2-5 minutes to let any additional liquid drain.
Lift the colander out of the bowl. Pour off any watery type liquid that is at the top of the bowl. Save the beige paste at the bottom. This paste is potato starch and will help the latkes stick together. Scrape up the paste and place into the potato mixture. Mix together with a large spoon.
In another bowl, mix the egg yolks, matzoh meal (or bread crumbs), 1 teaspoon of the kosher salt and the black pepper. Combine the egg yolk mixture with the potatoes and mix until well combined.
Place the egg whites in a clean, dry bowl. Use a whisk or mixer and beat the egg whites until they form and hold shiny peaks. Use a rubber spatula or wooden spoon and fold the egg whites into the potato mixture.
Pour the oil into a large, heavy skillet (a cast iron skillet works well) to a depth of 1/2 inch. Heat to medium-high heat; heat oil until a shred of potato mixture instantly sizzles when dropped in. Place several spoonfuls of the mixture into the pan, but do not crowd the latkes. After placing in the pan, flatten slightly.
Fry until deep golden brown, about 5 minutes, then flip over and continue frying until both sides are well browned, about 8 to 10 minutes for each batch. (You may need to add additional oil to fry subsequent batches.) Using a spatula, transfer latkes to the paper-towel-lined baking sheet. Blot any excess oil with additional towels.
If desired, dust with a little more salt and pepper. Serve immediately with sour cream and applesauce.