This recipe is gluten Free, vegetarian, and delicious.
Heat 3 tbsp olive oil in a large, heavy bottom skillet or cast-iron pan. Add potatoes and onion. Fry over medium heat until potatoes are tender; drain excess oil and set aside.
Beat eggs in a bowl and season to taste. Add potato and onion mixture; mix well. Check again for seasoning, and allow the potato mixture to sit in the eggs for at least 20 minutes.
Meanwhile, distribute the remaining olive oil among the heavy skillet and another pan that is slightly smaller in diameter. After 20 minutes, set both pans on separate burners over medium heat. Pour the egg mixture into the smaller diameter pan and cook until the eggs start to set.
Drain oil from larger pan and lock it into place on top of the other pan, then gently flip the pan over. Cook the tortilla on other side just until the eggs are fully set, and the surface becomes a lovely golden color.
Remove from heat and allow to cool until just slightly warm, or better yet, room temperature. Place a serving dish over the pan and flip onto platter to serve. Cut into squares and serve with aioli, if desired.