Preheat your oven to 375 degrees Fahrenheit

Fry up the potatoes: Get out a large oven-safe skillet and pour enough olive oil in it so that it covers the bottom by a ¼ inch. Place this over medium-high heat and fry the slices of potatoes in batches until they are slightly golden brown in color. Then use a slotted spoon to transfer these cooked potatoes to a large bowl and set aside.

Fry up the onions: Add the sliced onion into the same skillet and cook until they become translucent, but not browned. Once cooked, use a slotted spoon to transfer these onions to the same bowl as the cooked potatoes.

Drain off most of the oil from the skillet

Assemble the tortilla: Add the beaten eggs along with the salt & pepper to the bowl with the potatoes and onions. Then carefully mix and fold the ingredients until the eggs coat everything. Transfer this mixture to the same skillet and use either a spoon or fork to make sure everything is relatively flat.

Add the tortilla to your heated oven and bake it for 25 to 30 minutes, or until the top is nicely browned.

Once cooked take the tortilla out of the oven and carefully transfer it onto a cutting board. Then let it sit for 5 to 10 minutes before cutting into slices. Enjoy!