Spanish tortilla

Step by step

1. Peel the potatoes and slice them thin. If using onion, slice it thin too.
2. Heat the oil over medium in a 9 to 10 inch skillet. Cook the potatoes (and onion) with salt for 20 to 25 minutes without browning, until tender.
3. Drain well and save the oil.
4. Beat the eggs with a little salt, mix in the potatoes and let it sit 10 minutes.
5. Heat 1 tablespoon of the oil in the skillet over medium high. Pour in the mixture and let it set 3 to 4 minutes, loosening the edges.
6. Flip it with a plate and cook 2 to 3 minutes more. It should stay juicy inside.
7. Serve warm or at room temperature, cut in small squares.