Reprinted with permission from Spain: A Culinary Road Trip by Mario Batali with Gwyneth Paltrow, published by Ecco, an Imprint of HarperCollins Publishers, 2008.
Serves 4 to 6 as a tapa or appetizer
Tortilla espanola is essentially the national dish of Spain. You can eat it as a tapa, for breakfast, in a bocadillo (sandwich), or for dinner with salad and a bit of jamon. Basically anytime, anywhere. We had a great one at Valdubon and I think it's because they weren't afraid to use a lot of olive oil. No fear!
1/4 cup extra-virgin olive oil
1-1/4 pounds waxy potatoes, peeled and thinly sliced
1 medium onion, thinly sliced
8 extra-large eggs
Kosher salt and freshly ground black pepper
1. Heat the oil in a large cast-iron or nonstick skillet over medium-high until very hot but not smoking. Add the potatoes and onion, season with salt and pepper, reduce the heat to medium, and cook, stirring occasionally and adjusting the heat if necessary so that the vegetables do not brown, until the potatoes are tender when pierced with the tip of a parking knife, 15 to 20 minutes.
2. Meanwhile, beat the eggs with salt and pepper to taste in a large bowl. Add the potatoes to the eggs, then pour into the skillet, spreading the potatoes evenly in the pan. Cook for about 1 minute, just to set the bottom of the egg mixture. Reduce the heat to medium-low and cook for 20 minutes, or until almost set through. Carefully flip the tortilla over (invert it onto a plate if you must, then slide it back into the pan, bottom side up) and cook for 5 minutes longer, until set. Flip out onto a clean plate and allow to rest for 5 minutes. Serve warm or at room temperature.
After reducing the heat to medium-low in Step 2, start checking for doneness after about 15 minutes. It may not take the 20 minutes mentioned depending on the pan you use. You don't want to overcook the eggs or they'll toughen and become dry.
You could, of course, gild the lily with cheese. Grate some good Cheddar, a nutty Gruyere, Manchego or Parmigiano-Reggiano and toss into the egg and potato mixture. It isn't traditional but it adds another layer of flavor.
Use organic eggs if possible. There is a difference, especially in dishes like this one where eggs star.