Prep the Potatoes and Onion:

Heat the olive oil in a large skillet over medium heat. Add the sliced potatoes and onion, season with salt, and cook, stirring occasionally, until the potatoes are tender but not browned, about 15-20 minutes.

Beat the Eggs:

While the potatoes and onion are cooking, beat the eggs in a large bowl and season with salt and pepper.

Combine Eggs and Potatoes:

Once the potatoes and onions are cooked, use a slotted spoon to transfer them to the egg mixture (to avoid excess oil). Mix gently and let it sit for about 5 minutes.

Cook the Omelette:

Remove most of the oil from the skillet, leaving a thin layer. Return the potato and egg mixture to the skillet, spreading it evenly. Cook over medium-low heat, gently shaking the pan occasionally to prevent sticking. When the edges are set but the middle is still slightly runny, invert the omelette onto a plate, then slide it back into the skillet to cook the other side.

Serve:

Cook until the eggs are set and the bottom is golden brown. Slide the tortilla onto a plate and let it cool for a few minutes. It can be served warm or at room temperature, cut into wedges or cubes.