Begin by peeling the potatoes and giving them a thorough rinse under cold water. Using a sharp knife or a mandoline, slice the potatoes into thin rounds, approximately 5 mm thick. After slicing, pat the potato slices dry with paper towels, then place them in a large bowl. Season generously with salt and toss to ensure even coating.

In a large frying pan, heat about ½ inch of high-quality extra virgin olive oil over medium-low heat. Once the oil is sufficiently heated, add the potato slices, ensuring they are fully submerged in the oil. Add more oil if necessary. Allow the potatoes to cook slowly over low heat for around 20 minutes. It’s normal if they start to break down slightly during cooking.

While the potatoes are frying, crack the eggs into a large bowl and whisk them until smooth. Season with a pinch of salt.

Meanwhile, thinly slice the onion and fry it in a separate pan with a little oil over medium heat. Stir occasionally as the onion cooks down and begins to caramelize, a process that should take about 10 to 20 minutes. To prevent burning, deglaze the pan occasionally with a splash of water. Once caramelized, drain any excess oil and add the onions to the beaten eggs.

After the potatoes have cooked, remove them from the pan using a skimmer or spider, transferring them to a colander. Allow the potatoes to cool and drain for at least 5 minutes. Once they’ve cooled, gently fold the potatoes and caramelized onions into the egg mixture, ensuring everything is well combined. Let this mixture rest for 15 to 20 minutes to allow the flavors to meld.

Pour the remaining frying oil from the potatoes into a container for future use. Return the frying pan to the stove and set it over medium-low heat. Pour the egg, potato, and onion mixture into the pan. Cook the tortilla gently over medium-low heat for about 6 to 8 minutes, taking care not to rush the process to avoid a rubbery texture. Use a rubber spatula to loosen the edges of the tortilla as it cooks.

To flip the tortilla, place a large plate over the pan, then swiftly invert the pan so the tortilla lands on the plate. Some of the uncooked egg mixture may spill out, but this is normal. Slide the tortilla back into the pan to cook the other side, allowing it to cook for an additional 6 to 8 minutes.

Once fully cooked, slide the tortilla onto a serving plate. Allow it to cool slightly before slicing and serving.