Tortilla de patatas
Tortilla de patatas (potato omelette) is also sometimes called tortilla espaņola (Spanish omelette) to differentiate it from the dish commonly known as tortilla francesa (French omelette) or just tortilla, which is made only with eggs. It is a very popular dish at any kind of event in Spain and can be served either cold or hot. Although potatoes and eggs are the basic and in most cases the only ingredients of a tortilla de patatas, other vegetables can also be found accompanying it such as onions and, more rarely, red peppers, chives, artichokes, ...
See tortilla for the American variety.