Tortilla Espanola

? – 1 cup olive oil (use plenty, it is strained later)
4 baking potatoes, peeled and sliced 1/8 inch think
1 large onion, thinly sliced
salt and pepper
4 eggs

Heat oil in skillet over medium heat. Add potatoes and onions and cook about 15 minutes, stirring frequently to prevent them from sticking to each other. The pan will be crowded. Cook until tender and golden brown. Strain, reserving oil.
Whisk eggs and season to taste with salt and pepper. Stir the potato and onion mixture into the eggs. It is OK to stir the eggs in while the potatoes are hot.
Wipe out skillet well. Add three tablespoons of reserved oil and place over high heat. Add egg and potato mixture and reduce heat to medium. Shake pan frequently to ensure tortilla is not sticking. Cook for about 10 minutes or until the bottom is golden brown. The flavor will be stronger if browned slightly.
Place in a 325 oven for about 15 minutes or until the tortilla is cooked through. Remove and let rest for about 15 minutes before serving.
Serve with Herb Aioli
Variations: Stir in or layer roasted red peppers, cooked spinach, cheese, etc.
There is no need to flip the tortilla because it is baked at the end.

(from L?Academie de Cuisine, Tapas class)