Fill a large pot with water, add Salt (2 tablespoon) and bring to a boil.
Peel the Yukon Gold Potato (4).
Cut the peeled potatoes in half, then slice into 1/8 to 1/4 inch slices.
Add the potatoes to the boiling water and cook, stirring occasionally to prevent sticking, until a knife blade easily pokes through the potato, about 10 minutes.
Remove potatoes with a slotted spoon onto a plate and set aside to cool.
Quarter the Onion (1).
Cut onion quarters into 1/4 inch slices.
Thinly slice the Garlic (4 clove).
Saute onions in Extra-Virgin Olive Oil (to taste) over medium heat until they begin to soften, about 3 minutes. Add garlic slices and continue cooking for 2 additional minutes. Do not allow them to brown.
Remove onions and garlic from pan and set aside on a plate to cool.
Whisk Egg (7) in large bowl and season with Salt and Pepper (to taste).
When vegetables are cool, add the onions, garlic, and potatoes to the egg mixture and stir gently with a spatula until combined.
Prepare two medium sized non-stick pans, preferably one slightly bigger than the other, by coating with a layer of Extra-Virgin Olive Oil (to taste) making sure to coat the sides. In the smaller pan, pour in enough olive oil to cover the bottom. This is the one you will start with.
Warm the larger pan on low heat. Heat the smaller pan on high heat until just before the oil begins to smoke, then reduce to medium-low heat. The pan needs to be hot enough to set the eggs as soon as they hit the pan, but not so hot as to burn the tortilla.
Pour the egg/potato/onion mixture into the pan and smooth down the potatoes on top so that they are covered with egg.
Cover with the larger pan (or a lid) to retain heat. Every few minutes, run a spatula around the edges to keep the tortilla from sticking.
When the egg is firmly set around the edges but still jiggly in the center, about 15 minutes, place the larger pan on top and invert both pans so that the tortilla flips into the larger pan.
Bring the tortilla back up to medium-high heat to cook the bottom side. In the meantime, wipe the smaller pan clean and re-coat with Extra-Virgin Olive Oil (to taste).
When the bottom is cooked through, about 3-5 minutes, flip the tortilla back into the smaller pan and cook for 1-2 minutes to reform the shape.
Slide or flip the entire tortilla onto a plate. Serve warm or at room temperature.