Spanish Omelette with Potatoes and Onion

Method

1. Peel the potatoes and onion.
2. Cut the potatoes in half, then each half in half again. Slice into even pieces about 1/4 inch thick. Do not soak in water to preserve starch.
3. Cut the onion in half and slice into similar thickness pieces.
4. Combine sliced potatoes and onion in a bowl. Season with a pinch of salt and mix well.
5. Pour 1/2 liter of olive oil into a high-sided pan. Test the oil by adding a piece of potato and onion; when they sizzle, add all the vegetables.
6. Cook on low heat for 20 minutes, stirring occasionally, until potatoes are tender and slightly crispy.
7. After 20 minutes, drain the potatoes and onions from the oil using a slotted spoon, reserving the oil.
8. In a separate bowl, crack 6 eggs and beat them lightly until just combined; the whites and yolks should still be slightly separate.
9. Add the drained potatoes and onion to the eggs. Season with salt and mix gently.
10. Heat a small amount of the reserved oil in the same pan over low heat. Test with a drop of the egg mixture; if it puffs up immediately, the oil is ready.
11. Gently pour the egg mixture into the pan. Cover and cook on low heat for 8 minutes, until the bottom is set and golden.
12. Carefully flip the tortilla by sliding it onto a plate, then sliding it back into the pan. Cook the other side covered for another 8 minutes on low heat.
13. Serve hot or cold. The tortilla is best when soft in the center and crispy on the edges.