Peel and rinse the potatoes under cold water. Slice them into thin slices, about 1/2 centimeter thick (a mandolin is recommended for best results).

Pat the potato slices dry and place them into a large bowl. Sprinkle with salt and mix well.

Heat 1/2 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. Add more oil if necessary until all potatoes are covered. Cook for 20 minutes over low heat.

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

Slice the onion as thin as possible (julienne style). In a separate heavy pan, fry the onion over low heat 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 from the pan with a slotted spoon and place them into a strainer. Allow them to cool while excess oil drips away.

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

In the same pan where you fried the potatoes, remove all the 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.

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