Heat vegetable oil in a large skillet over medium-high heat. Once it is hot, add the onion and potatoes. Make sure the onion and potato slices are well-covered; add more oil if necessary. Cook for 20 minutes until soft. Drain the oil after the onion and potato have finished cooking.

In a large bowl, scramble the eggs. Add in the onion and potato slices. If the potato slices look too large, you can mash them a bit with a wooden spoon. Add in the salt and stir until the mixture is thick and even throughout.

Heat the olive oil in a non-stick skillet with high sides on medium heat. I used a 9" skillet so that it would come out about 2" thick. Pour in the egg mixture and cook for 4-5 minutes.

Once the bottom is golden brown, flip the tortilla over onto a flat plate and slide it uncooked-side-down back into the pan. This is the tricky bit, but it actually holds together pretty well so be fearless and just go for it! Cook for another 4-5 minutes until the bottom is golden brown as well.

Remove the tortilla from the pan and serve in slices (like pie). This is a great brunch food and actually reheats pretty well in the microwave if you make it for breakfast and want a slice later. This is typical in bars in Spain, they will cut slices and reheat them throughout the day rather than making a fresh tortilla each time.

I got the original recipe from the website below. I increased the number of potatoes and eggs to fit in my skillet - it's supposed to be a thick, hearty slice of tortilla rather than a thin omelet. http://www.foodnetwork.com/recipes/tortilla-espanola-spanish-omelet-recipe0.html

I would love to hear some tips about how to prepare this as well as variations on the basic recipe! I have seen some people using olive oil instead of vegetable oil to cook the potatoes and onions, which do you think is better?