You need yellow potatoes, yellow onions, eggs, salt, olive oil, and salt. A saute pan, a deep pan (stockpot), and a wide plate, wider than the saute pan to turn the tortilla --this is actually the most challenging step. Depending on size of the nonstick saute pan you want to use, measure how many whole potatoes will fit in the pan. Then use about a 1:4 ratio of onions to potatoes. Set the saute pan aside. You will use this later.
5 Medium yellow potatoes
2 Medium yellow onions
1/2 cup of olive oil
9 inch skillet (nonstick preferred)
Peel potatoes and slice them about 1/8 of an inch. I recommend using a mandolin for this but it is not necessary. Then peel and slice onions in strips.
Use the deep pan (stockpot) to fry the onions and potatoes. Start with a generous pour of olive oil, then throw onions when hot. After about a minute follow up with the potatoes and mix pretty constantly until potatoes begin to break and sides start to brown about 30 to 60 minutes. You will need to add olive oil to make sure things are frying. Fry until onions are caramelized and you can see some brown on the potatoes. Add salt to taste. Transfer potatoes to a bowl and allow to cool for 5 min. Break and scramble some eggs in a separata bowl add salt. Pour the potatoes and onions into the bowl with the eggs and mix well. There should be enough egg liquid to almost cover the fried potatoes and onion mixture.
Turn on the fire under your skillet, add oil. Once the pan is hot, pour the potatoes, and eggs mixture into pan and tap to arrange the top so it is flat, pushing any potatoes in and making sure egg mixture is well distributed. Cook until desired temperature, depending on how well done you like your Tortilla. I leave mine for about one minute then cover with plate larger than the pan to flip. Using your strong hand to hold the pan handle and you other hand to press the plate onto the pan, flip the pan and plate so plate is underneath and the tortilla sits on the plate. Put the pan back on the stove flame and carefully slide the uncooked side of the tortilla back from the plate into the pan. Fry for 2 or 3 minutes and slide the tortilla from the pan onto a clean serving platter.
Let the tortilla rest at least 15 min before eating.