The Tortilla Espanola or Spanish Omelet is the . .

The Tortilla Espanola or Spanish Omelet is the most commonly served dish in Spain. It is also called Tortilla de Patata or Potato Omelet. It is a typical Spanish dish consisting of a thick egg omelette made with potatoes fried in olive oil.
The potatoes, ideally a starchy variety, are cut into thin slices or in small dice. They are then fried in olive oil together with sliced onions at a moderate temperature until they are soft, but not brown. Browning is often avoided by using an excess of olive oil, which can later be strained and re used. The potatoes and onions are then removed, drained, and mixed with raw beaten and salted eggs. This mixture is then returned to the pan and slowly fried. The tortilla is fried first on one side and then flipped over to fry on 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 (triangle) portions (pincho de tortilla).