Peel the potatoes, cut them in half lengthwise, then cut in half again while the flat side on the cutting surface. Slices potatoes into thin slices.

Add olive oil to a 9-inch (23cm) skillet, heat over medium-high heat. When the oil is hot, add sliced potatoes and fry for 2-3 minutes, then add sliced onion. Cook over medium heat, stirring occasionally, for about 10-15 minutes, until potatoes are fork tender. Do not overcook.

Drain the potatoes and reserve the oil. Let cool slightly.

In a large bowl beat the eggs with salt. Add potato and onion and toss to coat. Let mixture sit for about 20 minutes.

In the same pan where you fried the potatoes, pour back 2 tablespoons of the reserved oil and heat. Pour potato mixture into the pan, cook on medium heat for 6-8 minutes. When the bottom is cook, flip the tortilla, using a big plate, and slide it back to the pan. Run a rubber spatula or a wooden spoon along the outer edges of the tortilla. Cook for 2-3 minutes, until the omelette is set but still a bit runny on the middle.

Slide the omelette onto a plate and serve.