Add olive oil to a large skillet over medium heat.

Add diced onion to the skillet and cook until translucent.

Add the sliced potato to the onion and season with about 1 1/2 teaspoon sea salt. Toss the potatoes around with the onion and olive oil to spread the salt around.

Crack the eggs into a bowl, season with the rest of the salt. Whisk the eggs together. Pour the beaten eggs into the skillet over the potatoes and onions.

Cook over medium high heat for 1 minute. Reduce heat to medium-low and cook for another 5 minutes.

Run a rubber scraper along the outer edge of the tortilla to keep it from sticking to the pan and to help it keep its shape.

Once it starts to firm up around the edges and in the center, place a large plate (one that is larger than the size of the pan) over the pan and flip the omelette onto the plate.

At this point, the cooked side of the spanish omelette should be on top.

Carefully slide the omelette back into the pan. Use the spatula to press the sides of the omelette in, to keep the rounded edge.

Cook on medium high heat for 1 minute, and change to low heat for 2-3 more minutes or until done. It will be done when it feels set in the center and a knife or toothpick inserted into  the center comes out clean.

Flip the finished spanish tortilla back onto a plate. Serve warm or at room temperature.