These are approximate instructions for how my landlord, Maruja, makes them. This is how she showed me to do it, and she usually makes this at least once when she has guests come. I am an exchange student studying physics in Zaragoza (Saragossa) Spain.
several potatoes (maybe 3 medium ones, maybe different)
3 large or medium eggs (less if you use less potatoes)
roughly ½ of a medium or large onion
A few tablespoons of milk
Peel the potatoes and chop them into thin pieces. Put them in a nonstick frying pan with a lot of olive oil. Add in some salt and heat. Chop the onion into small pieces and add them too. Cook with the lid on stirring occasionally for about 20 minutes, until the potato is cooked. While this is cooking, beat the eggs in a bowl and beat in a splash of milk. When the potatoes are tender drain out most of the oil into a cup. There should be still a little oil in the pan afterwards or else the tortilla may stick. Sometimes she puts some back in, sometimes not.
Pour the egg mixture on top of the potato-onion mixture and quickly spread it out with a spoon or a spatula to make it roughly even. Cook for a couple of minutes on the stove until mostly cooked through. It will still be runny and raw on the top when you flip it over.
To flip it over, put the lid of the pan on top of the pan and invert it. Then remove the pan and, assuming the tortilla has fallen onto the lid, place the pan right side up back on the stove and slide the tortilla into it. Cook for perhaps 2 minutes until it is cooked through. Some people prefer it softer, and some people prefer it slightly browned.
Serve immediately or later at room temperature. Will keep for a few days covered at room temperature. Maruja sometimes serves it with homemade mayonnaise. It is also popular to make leftover pieces into sandwiches.
There are other variants of this that Maruja has told me about. This is the “standard” one. When I came home I substituted crushed garlic for onions when I made it. This is not the kind she usually makes but she tells me that people do do it that way and it is pretty good too. She also says there is a kind with artichokes but I have never had it.
Written Sunday, March 5, 2017