Grate the potatoes and onion using a food processor or hand grater with a coarse grating disc. Place the grated mixture on a clean dish towel, then squeeze and wring out as much liquid as possible. Combine the baking powder and flour in a bowl.

Quickly transfer the mixture to a large bowl. Add the eggs, the flour and baking powder mix, salt, and pepper, and stir until the flour is fully incorporated.

Pour about ¼ inch of oil into a medium heavy-bottomed pan and heat over medium-high. Once the oil is hot (a drop of batter should sizzle when placed in the pan), use a heaping tablespoon to drop the batter into the pan, cooking in batches. Flatten and shape the batter into discs with a spatula. Cook until the edges of the latkes are brown and crispy, about 5 minutes, then flip and cook the other side until deeply browned, about another 5 minutes. Transfer the latkes to a paper towel-lined plate to drain and sprinkle with salt while still warm. Repeat with the remaining batter.