Peel and rinse the potatoes under cold water. Slice them into thin slices, about 0.5 centimeter thick (use a mandolin for best results).

Pat the potato slices dry, place them in a large bowl, sprinkle with salt, and mix well.

Heat 0.5 inch of high-quality extra virgin olive oil in a large frying pan over medium-low heat.

Once the oil is hot, add the potatoes, adding more oil if necessary until all are covered. Cook for 20 minutes over low heat.

While the potatoes cook, beat the eggs in a large bowl and season with salt.

Slice the onion as thin as possible (julienne style) and fry it over low heat in a separate heavy pan for 10-20 minutes until caramelized, stirring often.

When the onions are caramelized, drain off any excess oil and add them to the egg mixture.

Remove the cooked potatoes with a slotted spoon into a strainer and allow them to cool while excess oil drips away.

Add the drained potatoes to the egg mixture and stir well. Let the mixture sit for about 20 minutes.

In the same pan where you fried the potatoes, remove all oil. Over medium-low heat, add the egg and potato mixture.

Cook the tortilla for about 6-8 minutes per side over medium-low heat. Run a rubber spatula along the edges to prevent sticking.

To flip, place a large plate over the pan and quickly invert the pan onto the plate.

Slide the tortilla from the plate back into the pan to cook the other side.

Slide the cooked tortilla out of the pan onto a serving plate and let it cool a little before serving.