Spanish omelette

Spanish omelette or Spanish tortilla is a traditional dish from Spain. It is celebrated as one of the most popular dishes of the Spanish cuisine. It is an omelette made with eggs and potatoes, usually including onion. It is often served at room temperature as a tapa.
It is commonly known in Spanish-speaking countries as tortilla de patatas, tortilla de papas, or tortilla española.
The first reference to the tortilla in Spanish is found in a Navarrese document, as an anonymous "mousehole memorial" addressed to the court of Navarre in 1817. It explains the sparse conditions of Navarre's farmers in contrast with those in Pamplona (the capital) and la Ribera (in southern Navarre). After listing the sparse food eaten by highlanders, the next quote follows: "…two to three eggs in tortilla for 5 or 6 [people] as our women know how to make it big and thick with fewer eggs, mixing potatoes, breadcrumbs or whatever."
According to legend, during the siege of Bilbao, Carlist general Tomás de Zumalacárregui invented the "tortilla de patatas" as an easy, fast and nutritious dish to satisfy the scarcities of the Carlist army. Although it remains unknown whether this is true, it appears the tortilla started to spread during the early Carlist Wars.
Another tale is that the recipe was learnt by Spanish prisoners captured after the Battle of Montes Claros during the Portuguese Restoration War in 1665. After the Portuguese victory, more than 6,000 Spanish soldiers were kept in captivity for three years until the 1668 Treaty of Lisbon was signed. Upon their release, these prisoners brought part of the culture of Alentejo to Spain, including many recipes, which featured a potato egg pie that evolved into the modern version of "tortilla".
The word tortilla, which is the diminutive form of torta, literally means 'small cake'. In European Spanish and in some variants of Latin American Spanish, it means omelette. A potato omelette is a tortilla de patatas or papas.
As the dish has gained international popularity, and perhaps to distinguish it from the thin flatbread made out of wheat or maize popular in Mexico and Central America, the española or Spanish naming gained traction. As such, 'Spanish omelette' or 'Spanish tortilla' are its common names in English, while tortilla española is the formally accepted name even within the peninsula. In Spain, an omelette (made simply of beaten eggs) is known as tortilla francesa (lit. 'French omelette') to distinguish it from the potato version.
The Spanish omelette is widely available in Spain, and prepared in some Spanish-speaking countries.
The two main options are either with or without onion. The addition of onion is the cause of an unresolved dispute, pitting concebollistas (the "with onion" group) against sincebollistas (the "without onion" group, considering this to be authentic). It may be related to the tenderness of the local varieties of potato. Restaurateurs are expected to say whether their tortilla has onion, and industrial producers market both options.
The most common way to cook a Spanish omelette is as follows:
The omelette may be eaten hot, at room temperature, or chilled; it is commonly served, cut into bite-size pieces (pincho de tortilla), as a tapa, or cut into wedges.
Día de la Tortilla ("Tortilla Day") is a popular festivity celebrated in many towns in southern and western Spain. Its date varies depending on the town; however, it normally coincides with the Thursday before Lent, the first day of Carnival, also known as "Jueves lardero" (Fat Thursday). Many towns in eastern Spain have a similar celebration on that day. Traditionally, the inhabitants of each town go to a nearby rural area where they spend the day among family members and friends, eating Spanish tortillas and other foods, and playing games.