Preheat oven to 400 degrees F. Grease a 9-by-13-inch baking dish.
Thoroughly mix eggs, oil, flour, salt and pepper in a large bowl and set aside.
Peel and coarsely grate potatoes and onions in a food processor. Let stand 5 minutes, then divide the mixture into 3 to 4 batches. Wrap each in a kitchen towel and squeeze out the excess liquid.
Add the potato-onion mixture to the eggs and mix by hand until incorporated. Pour into greased baking dish and bake uncovered until brown and a toothpick, or knife, inserted in the middle comes out clean, about 1 hour.