Spanish Potato Omelet ( Tortilla española)

Walking through the streets in every town in Spain, in every bar, restaurant or fast food eatery you will find a well rounded potato omelet which is the one dish that every Spaniard will love to eat.  It does not matter if it is 11 in the morning, lunch or dinner, it can be eaten at any time of the day and in every corner of the country. 
It is amazing that that such a simple recipe, with so few ingredients can have so much taste.  The secret is in the olive oil and the amount of each of the three or four ingredients.  But this I will come back a little later.  First, like always I like to do a little research on the background and possible history of each of the recipes that I cook.
Tortilla de patata or tortilla española, the  earliest mention in the recipe books in Spain  dates from 1881 when Fidel Romero de Gallego writes about the dish in his "Hogar y Cocina sin desorden", published in Zaragoza. In page 40 it can be read:

Tortilla de patatas Fritas
Cuando estén fritas las patatas cortadas en ronchas delgadas, se echan los huevos y se hace por las regals de la tortilla sola. 

Which translates:

Fried Potato Omelet
When the potatoes are fried in thin slices, you add the eggs and you follow the rules of how to make a regular omelet.

The instructions are concise.  The truth is that when potatoes came in to Europe they were not a favorite of the wealthy people.  Omelets recipes go back to a couple of centuries before this first recipe from Fidel Romero, but they were filled with all varieties of vegetables and not potatoes.  Potatoes were ingredients that the poor people ate.  Therefore, it is likely that the Spanish potato omelet did exist much earlier than  1881, it is just that it remain a recipe of the low class, the peasants and the hard working  part of Spanish society. 
Today " La tortilla española" is on the table of every rich, poor, elegant and  not so elegant Spaniard.

Ingredients
four to five large potatoes
Olive oil 1/4 to 1/3 cup
One medium yellow onion
salt to taste
four to five large eggs

In a frying pan place the olive oil  and heat.  Thinly slice the potatoes  and onion.  Add to hot oil and let cook stirring occasionally till it is golden.  Add salt to taste.
In a separate bowl beat the eggs and add a pinch of salt.  To the eggs add the cooked fried potatoes, draining the excess oil.  Soak well the potatoes into the eggs mixture.
In a separate smaller frying pan, add a tsp. of oil and add the mixture of potatoes and egg. Cook one side and turn over with a plate so that the other side cooks.  Do this process several times, back and forth till the middle of the Tortilla is cooked.
Serve hot or cold with bread or any other complimentary dish.