1 1/4 pounds red bliss potatoes, peeled and sliced 1/8 inch thick
1 onion, halved and thinly sliced
Kosher salt and freshly ground pepper
8 large eggs
Steps
Preheat the broiler. Heat 1/4 cup of the olive oil in a large cast-iron skillet. Add the potato and onion slices, season with salt and pepper and cook over moderate heat, stirring frequently, until the potatoes are tender, about 20 minutes.
In a large bowl, lightly beat the eggs and season with salt and pepper. Scrape the potato mixture into the bowl, being sure not to leave any in the skillet.
Return the skillet to the heat and add the remaining 2 tablespoons of oil. Add the egg mixture, spreading it out in an even layer. Cover and cook over low heat until the tortilla is set on the bottom but still runny on top, about 8 minutes.
Transfer the skillet to the broiler and cook until the top is set, about 2 minutes. Let cool slightly, then slide onto a plate. Cut into wedges and serve.