Peel the potatoes, wash them, and cut them into very thin, small pieces.

Use a wide but not too deep skillet (this makes it easier to shape the tortilla later). Turn on the heat, add the oil, and when it's hot, add the potatoes. Stir over low heat while you peel and chop the onion into small cubes. Add the onion and a generous pinch of salt to the skillet with the potatoes, stirring occasionally. When the potatoes are soft, turn off the heat. Drain off as much oil as possible and set aside.

In a large bowl, add the 8 eggs and another generous pinch of salt. Beat well. In a separate cup, mix the milk with the baking powder until dissolved, then add to the beaten eggs and mix together. Next, add the potatoes and onions and stir to combine.

Using the same skillet, add a little oil (just enough to coat the bottom so the tortilla doesn't stick) and heat over low. Pour in the mixture. Cook slowly so the inside cooks through without burning. Watch the edges, loosen them gently, and be patient. Move the skillet so the less-cooked parts are over the heat to cook evenly.

When the bottom is set, confidently flip the tortilla using a flat plate that's wider than the skillet. (The first flip can be tricky, but don't worry if it breaks a little—just reshape it with a spatula.) Poke the tortilla a bit to help it cook inside, and keep turning as needed. The first flip is the hardest; the rest are easier.

Tip: You can make a small hole in the side you'll flip down to check if it's cooked through. When you serve it, the holes will be on the bottom and won't show.

Done! Enjoy!