A Spanish tortilla is a great party dish. You can make it hours ahead and serve at room temperature. Serve it as an appetizer by itself, or cut it into smaller wedges and serve it with a number of other tapas.
1 cup olive oil
2 lb. Yukon Gold potatoes, peeled and thinly sliced
1 large Spanish onion, thinly sliced
6 large eggs
Kosher salt and freshly ground black pepper
1. In large skillet, heat oil over medium-high heat. Add potatoes and onion, reduce heat, and cook, gently stirring to separate, being careful not to break potatoes, until potatoes are soft and cooked through but not browned, about 30 minutes. Drain oil into a cup and set aside. Use a slotted spatula to transfer potato mixture to a large bowl.
2. In a separate bowl, lightly beat eggs and season with salt and pepper to taste. Pour eggs over potato mixture and gently press potatoes into eggs until covered. Set aside and let rest for 10 minutes.
3. In a 10-inch skillet, heat 2 tablespoons of the reserved cooking oil. When oil is hot, add potato mixture, spreading evenly; reduce heat to medium-low. Cook until edges are cooked and center begins to set, about 10 minutes.
4. To flip, cover skillet with large plate; place one hand on plate to keep in place and invert skillet. Return skillet to stove, add 1 tablespoon more of reserved oil if necessary, and slide tortilla back into skillet. Reduce heat to low. Continue cooking until tortilla browns on second side and center is firm. Slice and serve warm or at room temperature.