Tortilla is the diminutive form of torta, cake. This dish is called tortilla de patatas or tortilla española to distinguish it from the plain omelette or tortilla francesa.
Tortilla de patatas or Spanish omelette, in English, is widely eaten in Spain and in many of the Spanish-speaking countries. While there are numerous variations, the traditional, classic and worldwide accepted version is made with 3 ingredients only: eggs, potatoes and olive oil. Onion or chives may be included, even though the addition of the onion is controversial, usually related to the tenderness of the local varieties of potatoes or the subtle touch of sweetness that onion, slowly cooked in olive oil, brings to the dish.

You can find tortilla de patatas almost anywhere, here, and ranging from the pretty cheap (€3) portion cut from a big tortilla, previously cooked and displayed on the counter, to the special, juicy and freshly prepared, upon demand, individual portions, varying from €6 and up to €15 or even more.
In order to really enjoy a homemade tortilla de patatas with fresh ingredients, we choose one of the ‘neighborhood cuisines’ or cuines de barri, places designed to offer the authentic taste of the dishes to the local community.
And one of such places is Parlament Cuina de Barri, located in the beautiful district of San Antoni. The restaurant takes the name of the street. The interior is an eclectic mix of vintage items and contemporary design, and the specific of the kitchen is Mediterranean, using fresh, local products. Location set and tapa ordered, we can now return to the story of the dish.
the Origins of Tortilla de Patatas
The first reference to the dish is believed to have been found in an anonymous letter addressed to the court of Navarre dating from 1817. The letter details the poor conditions of the populations around Pamplona and the Ribeira, stating that many make do with only a few eggs cooked as a tortilla with potato, breadcrumbs and other simple ingredients to feed five or six people.
One popular tale states that it was an army general called Tomás de Zumalacárregui who first invented the dish, in Bilbao, as a cheap and easy way to feed his troupes during the siege of the city, and yet another version of the story states that it was in fact a poor farm wife who invented the dish, one day when the general visited their farm and requested to be fed.

The Preparation
For the preparation, the potatoes, ideally a starchy variety, are cut into thin slices or small dice. They are then seasoned and sautéed, usually in extra virgin olive oil (with sliced onions, if used, being added at this stage). These ingredients are stirred at a moderate temperature until they are soft but not brown. The potatoes (and onions, if included) are then removed, drained, and mixed with beaten eggs. The mixture is then returned to the pan and slowly fried, turning to both sides.

Variations
Seasonings – such as pepper, parsley or oregano may be added as well, or even other ingredients like diced cured ham, chorizo, tuna, shrimp or different vegetables – tortilla paisana, for instance, includes red pepper and peas. Furthermore, chefs have featured versions including luxury ingredients, such as truffle and foie gras. A modern variation on the use of fresh potatoes has grown in popularity in recent years, fostered by Catalan chef Ferran Adrià and using potato crisps instead. Since the traditional recipe requires finely sliced potato bathed and cooked in olive oil, the use of crisps may well be a clever shortcut and an interesting twist on the traditional recipe. As flavory or popular as these variations may be, they are not considered a classic tortilla de patatas. The inclusion of onion is as about as far as the traditional recipe allows to stretch.
Tortilla may be eaten hot or cold; it is commonly served as a tapa or picnic dish, either cut into bite-size pieces and served on cocktail sticks, or in triangular portions (pincho de tortilla) to be eaten as a finger food. A tortilla is almost always accompanied with bread and, sometimes, with fried pimientos del padron.