Spanish Tortilla

The spanish tortilla has nothing in common with the Mexican tortilla except its name, which comes from the Latin torta—a round cake. In its most basic form, the Spanish tortilla is a potato-and-egg frittata, or omelet, which derives most of its flavor from olive oil. Although the ingredients are simple and minimal, when made correctly—and there is a straightforward but very definite series of techniques involved—this tortilla is wonderfully juicy. And because it is better at room temperature than hot, it can and in fact should be made in advance. (How much in advance is up to you. It can be fifteen minutes or a few hours.)