When I first made tortilla Español, I would dice the potatoes and boil them in salty water. I think that's a perfectly fine technique—one glance at g**gle images will prove that many people do just the same—but it's not the technique for me anymore. I like to slice my potatoes thinly and then fry them until they are nearly potato chips. And of course, I salt the hell out of them immediately after pulling them from the oil. Unsalted potatoes are nice, but salted potatoes are much better. Don't wimp out on the salt. You want the thing to taste good, not save your life.
Purists will tell you that tortilla Español should not be baked, that it should be cooked entirely on the stove top over a low flame—and flipped once—which is totally fine and dandy, but the oven works well, even if it's less authentic. I start my tortilla on the stove top, over the lowest flame my burner can hold, and then I transfer it to a 250° oven once the egg on the bottom sets just a bit. When all of the egg is set, you can shove your tortilla under the broiler to brown up the top a bit. If you're into pretty tops, which I am, you should do this.
Results like this raise an important (and perennial) question about authenticity: how much does authenticity matter? There is authenticity of method and authenticity of flavor. Sometimes an authentic flavor cannot be produced without using the authentic method. Other times it can. The important thing to remember here is that a good cook is a good cook, which is to say that you can bet your ass that there are lots Spanish people out there making poor tortillas by authentic methods. Authentic is one of those words that foodies use in inverse proportion to their skill and their understanding of food and cooking. I just wanna put that out there on this rainy June day in Massachusetts.