Tortilla Española - Spanish Potato Omelette

1. Peel and slice the potatoes and the onion finely. Heat olive oil in a skillet and fry the potatoes and the onion over low heat. They should not get colored or hard.  Once cooked through and tender, drain over a colander and keep the oil.
2. Beat the eggs with salt, mix carefully with the potatoes. Heat part of the oil in a skillet and add the egg-potato mixture. Cook for approximately 5 minutes on each side. It should be golden on the outside and slightly soft on the inside. You can make one big omelette or two smaller ones. (It is much easier to flip over a smaller omelette, you can do it with the help of a bigger lid or a serving platter.
3. Potato omelette can also be cooked with tripes, with a clam sauce, with saffron sauce, green parsley and garlic sauce, etc. In the north of Spain, it is often found to be stuffed with tomato, lettuce, tuna fish, mayonnaise, etc.

You can also add other ingredients to it: chorizo sausage, fried peppers, spinach.