Heat 3 tablespoons of the oil in a sauté pan over medium heat. Sauté the onion and garlic until soft.
Lightly beat the eggs in a medium-mixing bowl. Fold in the onions, garlic and potatoes. Season with salt and pepper.
Heat the remaining 3 tablespoons oil in a non-stick pan. Pour the mixture into the heated pan and cook on one side for 4 minutes. Flip the tortilla into another non-stick pan the same size.
Bake the tortilla, covered, for about 10 minutes at 300°F.
Serve the tortilla with garlic aioli.