6 T olive oil
1.5 lbs Yukon gold potatoes (3-4 medium), peeled, quartered lengthwise, and cut crosswise into 1/8" thick slices
1 small onion, halved and sliced thin
1 t. table salt
1/4 t. ground black pepper
8 large eggs
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Optional:
4 oz Spanish chorizo (cured) or Portuguese linguica, diced and fried
4 thinly sliced scallions
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Toss 4 T oil , potatoes, onions, 1/2 t salt and pepper in large bowl until potato slices are thoroughly separated and coated in oil. Heat 2 T oil in a 10" non-stick skillet over medium-high heat until shimmering**. Reduce heat to medium-low, add potato mixture to skillet, and set aside bowl without washing. Cover and cook, stirring with rubber spatula every 5 minutes, until potatoes offer no resistance when poked with the tip of a knife, 22 to 28 minutes (it's OK if some potatoes break into smaller pieces).
Whisk eggs and remaining 1/2 t. salt in reserved bowl until just combined. Using rubber spatula, fold hot potato mixture (and chorizo/scallions, if using) into eggs until combined. Return skillet to medium-high heat, add 1 t oil, and heat until just beginning to smoke. Add egg/potato mixture and cook, shaking pan and folding mixture constantly for 15 seconds. Smooth top of mixture with rubber spatula. Reduce heat to medium, cover, and cook, gently shaking pan every 30 seconds, until bottom is golden brown and top is lightly set, about 2 minutes.
Using rubber spatula, loosen tortilla from pan, shaking back and forth until tortilla slides around freely in pan. Slide onto large plate. Top with another large plate and flip. Slide back into skillet. Tuck edges under. Return to medium heat and continue to cook, shaking gently every 30 seconds, until second side is golden, about 2 minutes longer. Slide onto cutting board or plate and allow to cool for at least 15 minutes. Cut into wedges. Serve with Patatas Bravas Sauce.
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**If using chorizo, brown in 10" skillet in 1 T oil (not the 2 T suggested below) until fat has rendered. Remove chorizo (leave fat) and continue...
