A well-made Spanish tortilla is so good, so satisfying in every way, that I would nominate it to the Great Food Hall of Fame, if only there were such a thing. It has nothing to do with Mexican flour or corn tortillas. If it has a relative, it would be the Italian frittata.
In Spain, the dish goes by two names: tortilla de patatas or tortilla española. The one thing I avoid calling it is a potato omelet (its English translation) since a Spanish tortilla is more about potatoes than eggs, and the word omelet doesn't really conjure up the right image. Besides, a tortilla is more robust and gratifying than any omelet—and infinitely more versatile. It tastes great whether served warm, cool, or at room temperature. It makes an excellent breakfast, lunch, dinner, snack, or crowd-pleasing tapa. (A tortilla is a sure hit at any party or pot luck.) It can be made ahead, it's reasonably fast cooking (45 minutes, start to finish), and it welcomes variations (see More ways to enjoy a tortilla). At my house, we rarely go more than a week without having one for supper. Taste the magnificent tortilla española for yourself, and you'll know why.
I learned how to make tortillas from my Spanish husband, Isidro, who can stroll into the kitchen, peel and slice some potatoes, chop about half as many onions, lightly beat five or six eggs, and with no apparent thought, turn out a perfect tortilla every time. He insists there's nothing to it, and I agree, now that I'm clued in to the few tricks he'd been keeping secret. Here's how to turn five fairly pedestrian ingredients—potatoes, eggs, onions, olive oil, and salt—into a dish that deserves more fame and glory than any other, except perhaps paella (yes, there's a theme here).