1 ¼ pounds Yukon Gold potatoes, 3 or 4 medium
1 medium onion
1 cup olive oil
Salt and freshly ground black pepper
6 extra-large or jumbo eggs
Thinly slice potatoes and onions; I like to do this with my food processor, and I leave the potato skins on. Heat oil in an 8- or 10-inch nonstick skillet (I use cast iron) over medium heat. Once the oil is hot, carefully drop in the potato and onion slices.
Cook, turning potatoes gently every few minutes, until they are tender when pierced with a small knife - be careful not to brown or overcook. As potatoes cook, beat eggs with some salt and pepper in a large bowl.
Pull potatoes from the oil and drain potatoes them on paper towels. Wipe out skillet, and heat over a medium for a minute. Add 2 tablespoons oil. Gently mix warm potatoes with eggs and add to skillet. As soon as edges firm up, after a minute or so, reduce heat to medium-low. Cook 5 minutes.
Insert a rubber spatula all around edges of tortilla to make sure it will slide from pan. The top will still be runny. Carefully slide out onto a plate. Cover with another plate, and holding plates tightly, invert them. Add another tablespoon oil to skillet, and use the spatula to coax tortilla back in. Cook 5 minutes, then slide from skillet onto a clean plate. Serve warm (not hot), or at room temperature. Do not refrigerate.