Place the olive oil in a large skillet and preheat over medium-low heat.
Add the potatoes and onion to the pan and cook for about 20 minutes, stirring occasionally until the potatoes begin to break down a bit.
Once the potatoes are cooked, place them in a heat-resistant colander to remove any excess oil.
Crack the eggs into a large bowl and beat with a fork for 30 seconds until fluffy. Add the potatoes and onion, season with salt to taste and beat for another 30 seconds until everything is well integrated.
Place the same skillet over medium heat with a little oil (left over from cooking the potatoes), pour the potato mixture with egg and cook for 5 minutes on that side, giving it a little shape on the edges with a rubber spatula.
After this, carefully flip the tortilla onto a plate and then put it back in the pan to cook on the other side for another 4-5 minutes or so, depending on how well done you want it. If you want it less done, it should be cooked for less time and vice versa.
When the tortilla is ready, carefully remove it from the pan and let it cool for at least 5 minutes before cutting it.