Here's the recipe for Spanish Tortillas:
7 medium all-purpose potatoes
1 white onion, thinly sliced
sunflower oil (it’s not the end of the world if you don’t have sunflower oil)
2 tsp. salt
Peel potatoes and cut in coarsely irregular chunks and place them in a frying pan with the onion. Add enough oil (half olive and half sunflower) to partially cover the potatoes and the onion. Cook covered over low heat for 15 minutes or until tender (the amount of oil used depends on the size of the pan).
Uncover pan, increase heat, and fry until the edges of the potatoes begin to brown.
Drain the oil out of the pan and add beaten eggs with salt; return to heat and cook until brown on one side, turn over and brown on the other side. Cut in squares or triangles and serve hot or cold.
Note, I divided this recipe by 3 for just the two of us, and we loved it!