Peel potatoes, rinse, and coarsely shred on a box grater, transferring to a bowl of water as you go. Shred onion into a fine-mesh colander, discarding any uneven chunks. Pour potato mixture on top and drain. Rinse and dry bowl.
Squeeze handfuls of potatoes and onion to remove liquid, then pile on kitchen towels. Wrap and wring well. Whisk eggs, flour, bread crumbs, 1 tsp. salt, and the pepper in dry bowl. Add potato mixture and toss with hands until evenly coated.
Preheat oven to 200°. Filling a 1/4-cup measure three-quarters full, scoop potato mixture onto baking sheets. Pour 3/4 in. oil into a large frying pan with sides at least 2 in. high. Insert a deep-fry thermometer and heat oil over medium-high heat to 350°.
Put a portion of potatoes on a wide metal spatula, press into a 3-in. cake, and push into hot oil with another metal spatula. Shape 3 more latkes, sliding into oil; cook, turning once, until browned at edges but still soft in center, 2 minutes. Adjust heat to keep oil between 300° and 350°.
Transfer latkes to paper towels, then to a wire rack over a rimmed baking pan. Sprinkle with salt and keep warm in oven. Repeat to make remaining latkes; use a second pan when the first is full. Serve with applesauce, crème fraîche, chives, and roe.
Make ahead: Hold latkes at room temperature up to 3 hours. Rewarm on rimmed pans in a 300° oven 10 to 15 minutes.
Note: Nutritional analysis is per serving.
The Frying Guide
USE THE RIGHT OIL: For shallow-frying latkes, Jenn Louis likes the flavor and good-for-you factor of olive oil. For deep-frying sufganiyot, she uses neutral-flavored rice bran oil or vegetable oil.
USE ENOUGH OIL: To cook food evenly, you need about 3/4 in. oil for shallow-frying and 1 in. for deep-frying.
WATCH THE TEMPERATURE: Between 300° and 350° for latkes and 275° and 350° for doughnuts gives you a crisp crust and tender interior. Too low, and food will suck up oil like a sponge. Too high, and it'll burn.
GET A GOOD THERMOMETER: Taylor's classic candy/deep-fry analog thermometer ($11; amazon.com) has a sturdy clip.