Shred the potatoes and the onion using the large holes on a box grater. Place the shredded potatoes and onion into a large dish towel and tightly squeeze over the sink to extract as much liquid as possible.
In a large bowl, whisk together the eggs, breadcrumbs, salt, baking powder and pepper. Add the shredded mixture and stir to evenly coat.
Heat the vegetable oil over medium-high heat in a 12-inch skillet. The oil will be hot enough when you drop a piece of shredded potato into the pan and it immediately sizzles. Drop large spoonfuls of the mixture into the pan, pressing lightly on the top to flatten them slightly. Cook until golden brown, about 2 to 3 minutes per side. Transfer to a wire rack placed above a double layer of paper towels.
Repeat with the remaining mixture. If the mixture becomes watery between batches, stir together to incorporate. Additionally, add more oil to the pan as needed to keep a thin layer of oil covering the bottom of the pan.
Serve the latkes warm with sour cream and a sprinkling of fresh parsley, or applesauce.