2lbsYukon Gold potatoespeeled, quartered, & cut into ¼-inch slices
1Yellow onion, sliced
2 ½tspKosher Salt
Peel, and cut the potatoes into ¼-inch pieces. Place them in a large bowl of water while cutting to prevent oxidization. Next, peel and slice the onions. You pretty much want everything relatively the same size in order to cook evenly.
Drain and then dry the potatoes using a cloth napkin to remove excess water.
Over medium-high heat, pour the oil to the skillet. Add potatoes, onion, and salt. Use a heatproof spatula to coat potatoes with oil. When oil begins to bubble, reduce heat to medium-low and cook, turning frequently, until potatoes are tender but not too browned, about 20 to 25 minutes.
Using a slotted spoon, transfer potatoes and onion to a large heatproof bowl. Add the eggs and stir gently to combine, prevent breaking up the potatoes. Strain oil into a glass jar, and wipe clean the skillet.
Heat 3 tablespoons of the reserved oil in the same skillet over medium-high heat. Add the egg-potato mixture and cook, stirring constantly but gently to keep potatoes together, until eggs begin to set. The eggs will look scrambled. Cook for about 2 minutes. Spread mixture in an even layer. Reduce the heat to medium-low. Preheat broiler to high.
Cook tortilla, shaking pan occasionally to prevent it from sticking, for about 12 minutes. Transfer skillet to oven and broil until top of the tortilla is just cooked, about 2 minutes.
Remove from the oven. Using oven mitts, invert a large plate over the skillet, and flip it while holding the plate firmly. Return the tortilla to the plate. Let sit at room temperature for at least 20 minutes and up to 2 hours before serving.
Optional, serve with jamón serrano (prosciutto), cut chives on top of the tortilla, and manchego cheese.