3 pounds russet potatoes, about 6
1 vidalia onion
1/4 cup breads crumbs or matzo meal
2 teaspoons baking powder
1/4 teaspoon freshly ground black pepper
2 tablespoons (or more) schmaltz (chicken fat; optional)
2-4 tablespoons (or more) vegetable oil
Preheat oven to 325°. Peel potatoes. Using the large holes of a box grater or the grater disk on a food processor, grate potatoes and onions. Transfer to a large kitchen towel. Gather ends of towel; twist over sink and squeeze firmly to wring out as much liquid as possible. Open towel; toss mixture to loosen. Gather towel; wring out once more.
Whisk eggs, breadcrumbs, salt, baking powder, and pepper in a medium bowl to blend. Add potato mixture. Using your fingers, mix until well coated. (Latke mixture should be wet and thick, not soupy.)
Line a large rimmed baking sheet with several layers of paper towels. Set a wire rack inside another large rimmed baking sheet; set aside. Heat 2 tablespoons schmaltz, if using, and 2 tablespoons oil (or 4 tablespoons oil if not using schmaltz; fat should measure about 1/8 inches) in a 12 inches nonstick skillet over medium-high heat. Drop a small amount of latke mixture into pan. If the fat sizzles around the edges, it’s ready. (Do not let fat smoke.)
Working in batches and adding more schmaltz and oil to skillet as needed to maintain 1/8 inches fat, drop large spoonfuls of mixture into pan, pressing gently with the back of a spoon or spatula to flatten slightly. (If mixture becomes watery between batches, mix to incorporate; do not drain.)
Cook latkes, occasionally rotating pan for even browning, until golden brown and cooked through, 2 1/2-3 minutes per side. (If small pieces of potato floating in the oil start to burn, carefully strain out.)
Transfer latkes to paper towel-lined baking sheet to drain, then transfer to prepared wire rack. Place sheet with latkes in oven to keep warm and crisp while cooking remaining latkes.
Serve warm latkes with applesauce and sour cream.