Tortilla Espanola

6 tablespoons extra-virgin olive oil
3 medium russet potatoes, peeled, sliced 1/8 inch thick
1 onion, halved and thinly sliced
Sea salt and freshly ground pepper
8 eggs

1. Preheat the broiler. Heat the olive oil in a large, well-seasoned cast-iron skillet. Add the potato and onion, season with salt and pepper and cook over moderate heat, stirring frequently, until the potatoes and onion are tender but not browned, about 10 – 15 minutes.
2. In a large bowl, beat the eggs and season with more salt and pepper. Pour eggs into skillet. Reduce heat to low.
3. Cover and cook until set on the bottom and edges, about 8 minutes. Transfer skillet to the oven and broil 8 inches from the heat until the top is cooked through, about 1 – 2 minutes.  Remove from oven. Run a knife around the edge of the tortilla and loosen bottom of tortilla with a metal spatula. Set a large plate over the skillet and invert the tortilla onto the plate. Cut into wedges and serve warm or at room temperature.