This classic dish is often cut into wedges and served as one of several tapas. We like to eat cold or room-temperature slices of this omelet on a baguette with cured ham and Aïoli.
Heat in a 10- to 12-inch ovenproof skillet over medium heat:
Add:
Cook, stirring, until the onion is soft and golden, about 10 minutes. Transfer to a large bowl. Heat in the same skillet over medium-high heat:
Add:
Cook until golden brown, 10 to 12 minutes. Transfer the potatoes to paper towels to drain. Set the skillet aside with the oil in it. When the potatoes are cool, sprinkle them with:
Add the potatoes to the onions in the bowl and stir in:
Toss to coat. Set a rack in the middle of the oven, preheat the broiler, and return the skillet to medium-high heat. When the oil shimmers, add the egg mixture and immediately reduce the heat to low. Let the omelet cook undisturbed for 3 to 4 minutes, until the bottom is golden and the egg is two-thirds to three-quarters set. Shake the skillet from time to time to make sure the omelet does not stick. If it does, slide a spatula under it to free it from the skillet. Transfer the skillet to the oven and broil until firm. Shake the omelet to loosen it from the skillet and slide onto a plate. Cut into wedges and serve hot or at room temperature with: