As stated earlier, the traditional Tortilla de Patata has onions, eggs, and potatoes. Some places serve it hot or cold, up to you. Sometimes they give you some mayo (in Spain most mayos has plenty of garlic, ali oli (sp)) I have been in tapas restaurants where they have plenty of versions of tortillas. From veggies. chorizo, jamon, to seafood like shrimp. Can tuna is also a popular addition. There are some places where they do "double layers". A regular tortilla, a "frosting" of can tuna and mayo, and another thin egg tortilla (no potatoes) on top. There are unlimited versions... I cook the traditional tortillas quite often. I personally like them a little runny (sp?), but I have noticed that the Americans that have eating mine, like them on the overcook side... I still think that they are pretty tasty when well done. I let the potato mix to cool a little bit before mixing it with the eggs as other posters mentioned. I have seen recipes that called for you to smash the potatoes and the eggs with a fork. Others just called to mix them a little bit. They required a lot of salt and good olive oil if you want to remember Spain Alex