- 3 pounds Yukon Gold potatoes (6-8), peeled, cut into 1/4″ slices
- 2 teaspoons kosher salt plus more
- 2 cups olive oil
- 1 medium onion, chopped
- 10 large eggs, beaten to blend
- Place potatoes in a large colander, sprinkle with 2 teaspoons salt, and toss to coat. Let stand for 30 minutes. Pat dry with paper towels.
- Heat oil in a large nonstick skillet over medium-high heat. Add potatoes and cook, turning occasionally, until crisp-tender, 10-15 minutes.
- Add onion to potatoes in skillet; cook until onion and potatoes are soft, 5-8 minutes. Using a slotted spoon, transfer mixture to a large bowl; let cool slightly. Strain oil into a heatproof bowl; set aside.
- Add eggs to potato mixture; season with salt. Wipe out skillet. Heat 1/4 cup reserved oil over medium-high heat (chill remaining oil for another use). Add egg mixture, arranging potatoes to submerge.
- Reduce heat to medium; cook tortilla until almost set (it will be slightly runny on top), 25-30 minutes. Invert onto a large plate. Slide into skillet browned side up. Cook until golden on bottom and cooked through, about 4 minutes more. Serve warm or at room temperature. Cut into wedges. DO AHEAD: Tortilla can be made 2 hours ahead. Let stand at room temperature.