Peel the potatoes, thinly slice them (~ 0.5 cm/0.2 inches), and rinse with cold water. Pat them dry, place them in a bowl, and sprinkle with half the salt.
Peel and cut the onion in half and thinly slice it.
Place a nonstick frying pan with the olive oil over medium/high heat. When the oil gets warm, cook the potatoes until soft and easily breakable. Remove from the pan and drain the excess oil from the potatoes in a colander.
In the same pan, cook the onions until soft and lightly caramelized. Remove and drain them in the colander.
In a large bowl, break and beat the eggs until frothy. Season with salt and pepper and add the potatoes and onions. Let the mixture sit for ~ 15 minutes.
Remove the oil from the pan (you can keep it in a jar for future use) and place the pan over medium/low heat. When hot, add the egg mixture.
Use a spatula to fold the edges and cook the tortilla for ~ 8-10 minutes per side. Tortilla needs to get a light browning before flipping it. Shake the pan and place the tortilla on a large plate.
Place the pan over the tortilla and flip it quickly. Place it back on the stove and when cooked on this side, slide it out of the pan.
Let the tortilla cool at the preferred serving temperature, slice into pieces and serve.
Enjoy