1lb or so potatoes, I like to use fingerling potatoes 6 eggs a smallish to mediumish onion lots of olive oil some chicken or vegetable stock A VEGETABLE. I've used a bunch of kale and a tomato here, but other things also work
First, preheat your oven to 350º. If you are using cast iron (AND YOU SHOULD), toss that puppy in there as you preheat.
Slice the potatoes thin, I go for 1/8". If you have a mandoline this makes it easier, otherwise this may be a good chance to practice your knife skills.
Ditto on the onion. salt the potato and onion slices and sorta toss them together.
When the pan is preheated, toss it on the stove and put in a bunch of olive oil. GOOD OLIVE OIL IS THE KEY. If you use (1) a non-olive oil such as corn or soy or peanut or (2) a low-quality olive oil, this will taste like poop. It's possible to find good quality olive oil that isn't super expensive, and it's an important life skill to be able to track some down and keep it on hand. Anyway. Add to this olive oil, once it's on its way to hot town, the potatoes and onions, stirring/flipping the stuff constantly to (1) get the oil up in there between all those thin slices and (2) prevent sticking, both ad- and cohesive.
Cook the potatoes and onions until they're all translucent. They won't all be cooked, and that is okay. Some of them will have some crispy bits, and that is also okay. Remove them all to a bowl.
Cut up and add your vegetable to the pan. In my case, it was kale, which you sort of massage and rinse and massage and rinse, then I like to do a chiffonade of it (again, knife skill practicing). Fry your vegetable inclusion til it's sorta mostly cooked. Put it in the bowl with the potatoes. Turn off the pan.
In another bowl, wisk the six eggs and about an eighth of a cup of chicken or veggie stock with a little olive oil and some salt and pepper. Whisk really well!
When the egg is ready, turn the pan back on. Add the potatoes and vegetable to the egg mix, mix it up, and pour it right in that hot pan. Cook on the stovetop for a couple minutes, shaking to get everybody settled, then put it in the oven.
Cook for about half an hour, or until it smells really great and you can easily put a knife through to the pan in the middle of the tortilla.
Remove, let cool a little, run a small spatula around the outside, and flip onto a plate. Eat now or later or all the time. Good hot, warm, lukewarm or cold.