Tortilla Española

Peel potatoes and slice thinly into 1/8-inch rounds. Slice onion thinly into rings or half-moons. Pat potatoes dry with paper towels to remove excess starch.

Heat 0.25 cup olive oil in a 10-inch skillet over medium heat. Add potato slices and onion; season with salt and pepper. Cook, stirring occasionally, until potatoes are tender but not browned, about 15–18 minutes.

Using a slotted spoon, transfer the potato-onion mixture to a plate, leaving as much oil as possible in the pan. Reserve 0.25 cup oil in the skillet; discard or save excess for another use.

In a bowl, whisk eggs until well beaten. Stir in the cooked potato-onion mixture, paprika if using, and additional salt and pepper to taste. Let sit 2 minutes.

Heat the reserved oil in the skillet over medium heat. Pour the egg-potato mixture evenly into the pan. Sprinkle with grated cheese if desired. Cook undisturbed until the edges pull away from the sides and the center is nearly set but still slightly jiggly on top, about 6–8 minutes.

To invert (optional for extra browning): slide the tortilla onto a large plate, then slide back into the skillet to cook the other side for 2–3 minutes. For a simpler finish, place the skillet under a preheated broiler for 2–3 minutes until the top sets and lightly colors.

Let rest in the pan or on a wire rack for 3–5 minutes. Slide onto a cutting board, garnish with fresh parsley if desired, and cut into wedges. Serve warm, at room temperature, or chilled.