Preheat the oven to 375°. Working in batches, place handfuls of shredded onions and potatoes in a clean kitchen towel and squeeze out excess liquid into a bowl, reserving the liquid. Transfer onion and potatoes to another bowl.
Let excess liquid sit to allow starch solids to settle to the bottom of the bowl, about 5 minutes. Pour liquid off slowly, leaving the solid potato starch in the bottom of the bowl. Discard liquid.
In another large bowl, beat eggs well then beat in oil, reserved potato starch, baking powder, salt, and pepper. Pour egg mixture over potato and onion mixture and toss to combine.
Brush a 9”-x-13” baking dish with oil and place in the oven to preheat, 5 minutes. Carefully, remove baking dish from oven and fill evenly with potato mixture.
Bake until golden and potatoes are tender, about 1 hour. Turn oven to broil and broil kugel until top is golden, about 2 minutes.
