Heat oven to 350°F.
By hand: Chop onions very finely and coarsely grate potatoes.
With a food processor: Blend onions in food processor with regular blade until finely ground. Switch to grating blade and grate potatoes.
Place onions and potatoes in a large bowl. Sprinkle salt, pepper and starch evenly over potatoes and toss together with two forks or your very clean hands.
Break eggs right on top and use forks or your fingers to work them into the strands.
Heat a ¼ cup oil or fat in a 10-inch cast-iron skillet over high heat until very hot.
Pour potato-egg mixture into pan carefully and spread evenly in pan.
Drizzle with last tablespoon of oil.
Bake in heated oven for 75 to 80 minutes, until browned on top and tender in the middle.
Serve in squares, either right from the skillet or unmolded onto a platter.
