I was lucky enough to observe my dear friend Laura, a Madrileña, make this Spanish tortilla for brunch one morning while on vacation eating our way through Miami, but I quickly decided I could eat this at any meal. As I suspected, she'd been making this quintessential Spanish comfort food the very same way since she was 10 and watched her mother and grandmother make it back home in Madrid. The aroma of olive oil-fried potatoes was appetizing enough for me. We served it to our friends alongside a simple green salad with cava-spiked fresh-squeezed OJ.
Brown chorizo in a dry medium skillet over medium heat for about 8 minutes or until cooked all the way through. Remove from pan with a slotted spoon and transfer to a paper towel-covered plate to drain.
Beat eggs in a large glass bowl and set aside.
Heat 1 cup of the olive oil in a large skillet over medium heat, then layer half the potato slices and onions evenly in the pan, turning once after 10 minutes or when edges begin to brown slightly. (It will take two batches to fry all the potatoes and onions.) When the first batch is golden brown, remove with a slotted spoon and transfer to the bowl with the beaten eggs and mix well to combine.
Repeat frying method with second batch of potatoes and onions, then fold into the egg-potato mixture along with the salt, chorizo and cheese. In another large skillet (or the same one used to fry the potatoes, washed, and dried), heat 3 tablespoons of olive oil over medium heat, then add egg-potato mixture and press down firmly with the back of a large spoon to create an even layer.
Cook for 5-7 minutes, then remove pan from heat and place a plate large enough to accommodate the tortilla over the pan and invert the tortilla onto the plate. Transfer back to pan and cook on the other side for another 5 minutes, then transfer to a serving plate. Slice into wedges and serve immediately.