Spanish
Peel the potatoes and cut them into slices about 3 mm thick; slice the onion thinly and toss both with half the salt.
Heat the olive oil in a 24 cm non-stick frying pan over medium heat, add the potatoes and onion and cook gently for 20-25 minutes, turning now and then, until soft but not browned.
Drain them in a colander set over a bowl, keeping the oil, and let them cool for 5 minutes.
Beat the eggs with the rest of the salt and a little pepper in a large bowl, fold in the potatoes and onion and leave for 10 minutes.
Heat 1 tbsp of the reserved oil in the pan over medium heat, pour in the mixture and cook for 5-6 minutes, shaking the pan, until the bottom is set and golden.
Put a flat plate over the pan, turn the omelette out onto it, slide it back into the pan and cook for 3-4 minutes more.
Let it rest for 5 minutes and serve warm or at room temperature, cut into wedges.