Peel the potatoes and rinse them under cold water. Slice them thinly using a sharp knife
Pat the potato slices dry with paper towels and put them into a large bowl, then sprinkle with salt and mix well.
Heat a ½ inch of high quality extra virgin olive oil in a large frying pan over medium low heat. When the oil is hot, add the potatoes and add more oil if necessary until all are covered.
Cook the potatoes on low heat for 20 minutes. They may break down a little; this is okay. You basically want to poach the potatoes but do not brown.
While the potatoes are cooking, beat the eggs in a large bowl and season with some salt.
Slice the onion thinly, and add them to the cooking potatoes.
Once the potatoes and onions have fried for 20 minutes, remove them with a skimmer or slotted spoon into a colander and allow them to cool and drain for at least 5 minutes.
Place potatoes and onions into a bowl and add the eggs. Gently mix well to coat the potatoes.
Pour out the frying oil from the potatoes and save it for another batch. Place the pan over medium-low heat and pour in the potato and egg mixture.
Cook over medium-low heat for about 6-8 minutes. Make sure the heat is low enough or the tortilla will cook too quickly and burn. You can run a rubber spatula along the edges to make sure the tortilla isn't sticking.
To flip the tortilla, take a large plate and put it over the pan and flip quickly. Slide the tortilla back into the pan to cook the other side, and cook for another 6-8 minutes.
Slide the tortilla out of the pan onto a serving plate and let cool 10 minutes before slicing and serving.
Feel free to add ham, vegetables, or any other inclusion before cooking tortillas - YUMMY!