Crack the eggs into a bowl. Whisk with a fork and add a pinch of salt.
Heat some oil in a frying pan (not one with a heavy base as this will prove to be a hindrance when preparing to do the flip).
Add the potato and fry for a couple of minutes. Add the onion and mash together.
When the potato starts to brown a little on the edges and is mashed up with the onion in a lumpy fashion then add the eggs. Make sure the potato and onions are fully submerged by the eggs. Poke the potato to allow some of the egg to seep into the mashed mixture.
Fry this gently on a low heat. While cooking shake the pan to loosen the tortilla from the base and tidy the edges up with a wooden spoon. Do not over cook. The middle is meant to remain runny and gooey.
The egg will start setting, as this happens place a plate over the pan, a large enough plate to cover the pan substantially, and with a quick co-ordinated movement of both wrists ?flip? the tortilla over onto the plate and slide back into the pan to cook the underside.
Keep shaking the pan lightly so the tortilla does not stick to the bottom.
Once it feels firm on the edges and soft in the middle (after about 1 minute) then slide the tortilla back onto the plate. For the brave heart you can do the flip again if you wish.
Let the tortilla rest for about 5 to 10 minutes before serving. Cut into cake slices or cubes. Garnish with green olives.