There’s an art to making a good tortilla, and I’m not sure I’ve cracked it yet (although I’ve cracked plenty of eggs trying). It’s the sort of thing where even the most detailed recipe is no substitute for being able to sense when you’ve got it right. Even if they aren’t up to the standards of the average Spanish tapas bar (can I do those rounded edges? Can I hell!), I have been pretty satisfied with my last couple of attempts.
The key points are a) the correct ratio of eggs to potatoes, and b) the right sized, heavy frying pan. I reckon you need about one medium potato per egg, but really you need to look at the mixture and know whether to add another egg. It should be neither too eggy (it won’t hold together) nor too packed with potato (too stodgy). The mixture should fill the pan to a depth of between 1 and 1 1/2 inches — thin tortillas are hopeless, and if it’s too thick it will scorch before it’s set in the middle.
Some people slice the potatoes, others cube them. I’m in the “slice them” camp at the moment, but I may change my mind. The onion is essential — it will be too bland without. The end result should be firm enough when cold to cut into wedges or squares and eat with your hands. At the same time it’s not nice if it’s so overcooked it’s gone leathery (another reason not to do a thin tortilla).
5-6 medium waxy potatoes
1 medium onion
salt and pepper
Slice the potatoes thinly and finely chop the onion. Heat a generous amount of olive oil in a heavy frying pan of an appropriate size — the oil should cover the bottom to a depth of about 2-3 mm. Place over a medium-low heat and add the potatoes; cook gently for about 5 minutes, stirring occasionally, before stirring in the chopped onion (if you add it earlier, it may burn). The potatoes and onions must be completely cooked before you add the eggs, but they mustn’t brown. This process should take about 20 minutes; keep checking and stirring.
When the potatoes are cooked, season with salt and tip them into a sieve over a bowl, letting the oil drip through. Beat the eggs in a large bowl with some salt and pepper. Add the drained potatoes and onions; this is the point where you need to stir it and decide whether the ratio is right, adding another egg or a bit more potato if necessary.
Pour some but not all of the oil back into the pan; you only need a thin layer to stop the tortilla sticking. Over a medium heat, pour in the egg mixture and let it cook for about 10 minutes, till it’s lightly browned on the bottom and no longer runny on top.
At this point you have a choice. Are you brave? If so, take either a plate a little larger than the pan, or a flat pan lid (i.e. no lip) of similar dimension, and place it over the pan. With oven-gloved hands, flip the whole lot over so that the uncooked side of the tortilla ends up on the plate. Then slide it back into the pan. Cowardly? Preheat the grill and slide the pan under it to finish cooking the top. Either way, it should only take another 3-5 minutes.
When cooked, slide onto a plate and leave to cool. I genuinely do think it’s nicest left in the fridge overnight; the flavour always seems much better the next day. It will easily keep a few days in the fridge. Eat in squares as a tapa, or with salad and bread as a main course.