Peel and cut the parboiled potato into thick slices.
Heat a large amount of olive oil in a pan and sauté the onion over medium heat.
Add the potato slices and chorizo and cook together until the potatoes are soft.
In a bowl, beat the eggs with a pinch of salt, ground white pepper, spring onions and 1 tbsp of olive oil until foamy.
Pour the eggs over the potatoes, stir gently to combine and cook the first side for 3-4 minutes with a fitted lid on top until the bottom gets golden brown.
Put a plate on top of the pan, hold it firmly and flip quickly. Slide the omelette back into the pan and cook the second side for 2-3 minutes for a soft tortilla.