Prepping the potatoes/onions

In an 8 inch thick bottomed frying pan, arrange alternate layers of potato slices, onion, salt and olive oil to cover. Repeat until ingredients are used up. Yes, it's a lot of olive oil. But you can save and reuse it after this (see next steps).

Slowly, very slowly on low heat (covered until heat comes up) cook the mixture until the potatoes are easily pierced, about 60 minutes. When ready, strain the cooked potato and onion through a colander, reserving the olive oil (you should save the olive oil for reuse).

Combining with egg

Beat the eggs lightly with a fork and combine with the potato/onion mixture. Set aside for 20 minutes - the potatoes and onions will absorb much of the egg while they sit.

Cooking the tortilla

Heat 1 tablespoon of the reserved olive oil a medium sized non-stick pan at medium high heat and pour in mixture. Shake pan to level contents. After 10 minutes when it seems the omelette is cooked halfway through, cover with plate large enough to cover, hold plate down firmly and quickly invert contents on to plate.

Quickly swipe pan clean with paper towel, add one more Tablespoon of the reserved olive oil and slide inverted omelette back into the pan to cook the other half. Repeat flipping process if you are not satisfied with how the omelette looks.

Serving

Set aside for at least 1/2 hour and serve warm or room temperature. Serve with ajiolli. If serving as a Tapa, cut into one inch squares.