In Spanish, this dish is called “tortilla de patatas” or “tortilla española” to distinguish it from a plain “omelette” (tortilla francesa, literally “French omelette”). Tortilla in origin meant just “small torte/cake”. These dishes are unrelated to the maize or wheat tortilla of Mexico and neighbouring countries, a thin flatbread.
The Spanish tortilla (Tortilla de patatas in Spain) is the most common gastronomic specialty found throughout Spain. While there are numerous regional variations, the most common version is the one made only with eggs and potatoes, and possibly onion. The addition of the onion is often controversial and usually related to the tenderness of the local varieties of potatoes. To avoid confusions some restaurants distinguish between the Tortilla de patatas (pure) and the Tortilla de patatas y cebolla (with onion).
Thinly slice 6-8 potatoes (ideally a starchy variety) and one or two medium sized onions (optional) and fry at a moderate temperature in an abundance of olive oil until they are soft, but not brown. Browning is avoided by using an excess of olive oil, which can later be strained and re-used. Strain the mixture into a clean bowl and mix with 6 raw beaten eggs and salt to taste. Heat a couple of spoons of the strained oil in a clean non-stick frying pan and slowly fry the mixture, first on one side and then flipped over onto its other side. Other ingredients, like green or red peppers, chorizo, tuna, shrimp or different vegetables, may also be added.
The tortilla may be eaten hot or cold; it is commonly served as a tapa or picnic dish throughout Spain. As a tapa, it may be cut into bite-size pieces and served on cocktail sticks, or cut into pie style (triangular) portions (pincho de tortilla).