
Grate the potatoes and onion on the largest holes of a box grater. (Alternatively, you can use the grating attachment of a food processor.)
Place the potato and onion mixture on a lint-free kitchen towel or a large piece of cheesecloth and squeeze out as much liquid as possible.
In a large mixing bowl, stir to combine the potato and onion mixture with the egg.
Sprinkle the flour, salt, baking powder and pepper evenly over the potato mixture. Stir it gently to combine well.
Meanwhile, fill a large, heavy-bottomed skillet with ¼-inch of oil. Heat it over medium-high heat to 350°F.
Working in batches, drop spoonfuls of the latke mixture, between 3 to 4 tablespoons in size, into the hot oil. Press gently with the back of a spoon or spatula to flatten their tops slightly. Cook for about 3 minutes until golden brown. Flip the latkes and cook for an additional 1 to 3 minutes until golden brown. (Adjust the heat as needed to maintain 350°F.)
Place the latkes on a paper towel lined plate or a wire rack set over a small, rimmed sheet tray. Repeat with the remaining potato mixture, adjusting the heat as needed.
Serve the latkes with sour cream and applesauce, if desired.