The oil is heated in a nonstick frying pan. Add the onions and peeled and cut into thin slices potatoes, then stir, add salt, cover with a lid and leave on low heat for 20 minutes. Drain them from the oil thoroughly.
Leave 1 tablespoon of oil in the pan. The remaining oil can be used for cooking. The eggs are beaten and mixed with the potatoes and onions. Season with salt and pepper.
In a well heated pan, pour in the mixture with eggs and potatoes and fry for 5 minutes on medium heat. Turn upside down in a large plate and return to the pan to fry on the other side for 5 minutes.
This is served cut into slices with fresh tomatoes.