Fill a large bowl with cold water. Peel potatoes and place into the bowl of water as you go to prevent them from browning.
If using a food processor: Once potatoes are peeled, cut them into large chunks so they fit into the food processor attachment. Use a food processor fitted with the shredding blade to shred the potatoes. Alternatively, use a handheld box grater to shred the potatoes. Then, shred in the onion as well.
Place the shredded potato and onion mixture into a cheesecloth or thin kitchen towel and wring out any excess liquid over a large bowl. Discard the liquid from the bowl, wipe it clean with a paper towel, and transfer to shredded potatoes/onion to the bowl.
To the bowl of potatoes, add the egg, potato starch, salt and pepper. Mix until well combined.
Prepare a plate or pan lined with 2 layers of paper towel for later. Set aside.
Heat oil in a medium-large skillet with high sides (I love a non-stick or cast iron skillet), on the stove over medium-high heat. To test if oil is ready, drop in a tiny piece of the potato mixture -- if it starts to sizzle, you’re set! If using an instant read thermometer, the oil should register about 370°F (188°C).
Lower the heat to a medium flame to prevent oil from splattering. Scoop the potato latke mixture into ¼ cup measuring cup and press down into the measuring cup to squeeze out any excess liquid (let excess liquid drain into the bowl or discard it). Place the latke mixture into the pan. Use a pancake spatula to lightly press down on the latke to flatten it very slightly. Only fry 3-4 latkes at a time to prevent overcrowding.
Fry latkes for 2-3 minutes per side, until both sides are crispy and golden.
Place each fried latke onto the prepared paper towel. Allow to cool 5-10 minutes before eating!
Serve latkes with a bowl of sour cream & chopped chives and/or applesauce.