Tortilla de patata, or potato omelet, a.k.a. tortilla española, is one of the most well-known Spanish dishes, and deservedly so: at its best it is really good. The best tortillas de patata, to my mind, are toasty brown on the outside and creamy-custardy on the inside. (The worst, on the other hand, are tough, dry, insipid, and heavy). As all tortillas de patata are essentially the same thing--eggs, onion, potato, olive oil and salt--the best quality ingredients and correct cooking are the keys to success.
A wedge of tortilla de patata is often served as a tapa in Spanish bars, though it's almost always better made at home. Esperanza, my mother-in-law, makes a truly excellent tortilla de patata. The recipe that follows is adapted from hers.
The common translation "potato omelette" has created some confusion, leading some English-speakers to think tortilla de patata is a breakfast dish. It is not. So far as I know, no one in Spain ever eats tortilla de patata for breakfast--except for tourists who make the mistake of ordering one from the menu first thing in the morning.
Tortilla de patata may be sliced into small wedges and served as a tapa or canapé.
Or larger pieces may be served as a main dish.
It is also often eaten as a sandwich, bocadillo de tortilla de patata, which is outstanding and the subject of a future post.
The word tortilla can also cause confusion because it is the same used for Mexican flatbreads. In Spain, tortilla always means some type of omelet.
Like the Italian frittata, which it resembles, tortillas can be made out of all sorts of things. Asparagus and mushrooms are popular. Esperanza often makes for me a tortilla de bacalao, salt cod, which I love.
Unlike the frittata, however, the tortilla is not finished-off in the oven, but flipped in a pan. This flipping maneuver can be tricky, but it's essential to the special texture and taste of a tortilla. So please do not finish off your tortillas in the oven. Learning the flipping technique isn't too hard, and it's well worth the effort.
For obvious reasons, it's best to use a non-stick pan, though I have made tortillas in very well-seasoned iron pans. In any case, choose a pan you're confident the tortilla won't stick to.
The size of the pan is also important. For the following recipe, which uses four eggs and two large potatoes, a small frying pan, eight inches in diameter, would be the right size. If you upped the number of eggs to six and used more potatoes, you would need a 9 1/2 or 10 inch pan. Your aim should be a tortilla about an inch thick or more.

You will also need a plate that fits neatly over the top of the pan so that you can flip the tortilla. You don't want the plate to be so large that it will be cumbersome to handle, but you don't want it too small, or it won't cover the pan completely, and the eggs will run out during the flip. The plate fitted over the pan in this picture is a perfect fit.

For those intimidated by the flipping maneuver, there are special hinged pans that can make flipping a tortilla easier. With these a plate is unnecessary. Click HERE to see a hinged, non-stick tortilla pan available at La Tienda. La Tienda also carries attractive ceramic plates designed for flipping tortillas.
Here's the recipe:
Ingredients:
2 large Idaho or russet potatoes (or three medium potatoes)
1 large onion
Olive oil
four of the best large eggs you can find
salt
Preparation
First peel and chop the onions.
Put two tablespoons of olive oil in a heavy frying pan, add the onion, and cook it slowly, stirring occasionally, until it's soft and slightly browned. This can take 15 to 20 minutes.

Meanwhile, peel the potatoes and cut them in two longways.
Slice the potato halves into 1/4 inch thick pieces.

Sprinkle them with kosher salt. Toss well.
When cooking the potatoes, you have a choice. You can fry the potato pieces in olive oil, as I describe in my post cooking French fries the Spanish way. (This is the traditional Spanish way of preparing potatoes for tortilla de patata). Or you can toss the potato slices with olive oil until they're evenly coated, arrange them in a single layer on a baking sheet, and bake them in a 400 degree oven for 25-30 minutes, or until lightly browned. Either method works fine. (The fried potatoes are not any more oily, by the way: see my post "How little oil potatoes fried the Spanish way absorb." Use whichever method is most convenient.)

Beat four eggs in a large bowl. Add the cooked onions and the cooked potatoes.
Stir.
I rarely add salt, as the salt I've put on the potatoes is usually enough.
Now heat up a non-stick frying pan. Wipe it down with olive oil. Pour the egg-potato mixture into the pan.
Let it cook over medium/medium-high heat. Give it a gentle shake now and then, and nudge the edges with a wooden spoon to make sure it's not sticking.

After five or six minutes (depending on how hot you have the pan) slide a plate over the frying pan. Hold the frying pan firmly with one hand and the plate in place with the other. I like to do this over a clean cutting board or some other clean work surface. That way, if there's an accident (as there sometimes is when flipping a tortilla de patata) it doesn't make a mess of the stove.

Now do the flip. Just turn the pan and plate together upside down in one quick, smooth motion.
If all goes well, the torilla should come out of the pan clean.

The raw side of the tortilla is now against the plate.
Wipe the pan down with a little oil and gently slide the tortilla back into the pan. Use a wooden spoon to nudge along any potatoes that try to stick to the plate.

Now return the pan to the burner.

Cook this side of the tortilla 5 minutes over medium/medium high heat. Give it a gentle shake now and then to make sure it's not sticking. Once again, do the flip. (It should be easier this time, as both sides of the tortilla are cooked).
Slide the tortilla back into the pan and return it to the burner a minute more. Flip it again, and continue until both sides of the tortilla are as toasted as you like them. Put the tortilla de patata on a nice plate and serve.
Tortilla de patata can be eaten hot or at room temperature. It's convenient for tapas parties because you can make it several hours ahead of time.