1 c. olive oil or a mixture of olive and other vegetable oil
4 lg. potatoes, peeled and cut in 1/8 inch slices
1 lg. onion, thinly sliced
Coarse salt
4 lg. eggs

Heat the oil in an 8 or 9-inch skillet and add the potato slices one at a time so they don't stick together. Alternate layers of potato with the onion slices and salt the layers lightly. Cook slowly over medium heat (the potatoes will really "boil) in the oil rather than fry), lifting and turning the potatoes occasionally, until they are tender but not brown.

The potatoes should remaining separated, not in a "cake." Drain the potatoes in a colander, reserving about 3 tablespoons of the oil. (The onion and potato give the oil a wonderful flavor, so save the rest for some other use.) Wipe out the skillet, scraping off any stuck particles. (If this is difficult to do, wash the skillet. It will be used again to set the omelet and must be completely clean to avoid sticking.)

Meanwhile, in a large bowl beat the eggs with a fork until they are slightly foamy. Salt to taste. Add the potatoes to the beaten egg, pressing the potatoes down with a pancake turner so that they are completely covered by the egg. Let the mixture sit for 15 minutes.

Heat 2 tablespoons of the reserved oil in the skillet until it reaches the smoking point. (It must be very hot or the eggs will stick.) Add the potato and egg mixture, spreading it out rapidly in the skillet with the aid of a pancake turner. Lower the heat to medium-high and shake the pan often to prevent sticking.

When the eggs begin to brown underneath, invert a plate of the same size over the skillet and flip the omelet onto the plate. Add about 1 tablespoon more oil to the pan, then slide the omelet back into the skillet to brown on the other side.

Lower the heat to medium and flip the omelet 2 or 3 more times (this helps to give the omelet a good shape while it continues to cook), cooking briefly on each side. It should be juicy within. Transfer to a platter and cool, then cut in thin wedges or into 1 to 1 1/2 inch squares that can be picked up with toothpicks. (May be prepared ahead.)

VARIATION: This tortilla is occasionally served in a sauce. To make the sauce, heat 1 tablespoon olive oil in a skillet and saute 1 small onion, finely chopped, and 1 clove garlic, minced, until the onion is wilted. Add 1 small tomato, chopped, turn up the heat, and cook for a couple of minutes. Stir in 3/4 cup chicken broth and a few strands saffron.

Cover and simmer for 15 minutes, then strain, pressing with the back of a wooden spoon to extract as much liquid as possible. Stir in pimento strips, cut from 1/2 pimento. Cut the tortilla in 1 1/2 inch squares. Place the sauce, cover, and simmer for 2 or 3 minutes. Cool to room temperature and serve.