Grate half the potatoes with the onion, drain and squeeze out all the liquid into a bowl. Blend the other half of the potatoes and drain too. Set bowl of liquid aside to allow the starch to settle at the bottom.
Mix the eggs, salt and pepper into the potatoes.
Pour the liquid from the potatoes out carefully to leave the white starch at the bottom, then add the starch to the potato mixture.
Fry the mixture in oil till browned and crispy, around 10 minutes.