In an 8″-10" non stick skillet, heat the olive oil in medium heat (6).
Add the onions and sweat them for about 2 minutes, until a bit soft but not brown.
Add the diced potatoes and pinch of salt, and mix, keeping the heat at medium for about 2 minutes.
Lower it to medium low (4) for about another 15-20 minutes. By the end the potatoes should be able to be mushed with a fork and you can do this a little bit if you want.
In a separate bowl, whisk together the eggs and another pinch of salt.
With a slotted spoon, remove the potatoes from the oil. Let the excess oil drip and add the potatoes to the eggs. It’s ok if they are hot and the eggs scramble a bit.
Remove most of the oil from the pan. Turn the heat back to medium (6). Add the egg mixture and using a wooden spoon, stir the center so the egg starts to cook. When the center starts to scramble, let it be and don’t stir anymore. Let cook for a few minutes.
THE HARDEST PART: Flip the tortilla with the help of a plate and finish cooking the other side. This flipping isn't the hardest part, rather transferring it back into the pan. That's why the first side needs to be cooked well and even slightly toasted.
When finished, depending on the consistency you want, let sit for 5 minutes before cutting, serving, and garnishing with chives.