A Spanish tortilla is just eggs, potatoes and onion, but the potatoes cook low and slow in olive oil first, which is what makes it worth the extra step. Traditionally it's served at room temperature, so it's good for using up potatoes already in the cupboard, and just as good made the night before.

Spanish Tortilla with Potatoes and Onion

Scale

Ingredients

1 cup olive oil you'll drain most of it off after cooking the potatoes; reserve 2 tablespoons for the pan
2 lbs potatoes, peeled and thinly sliced Yukon Gold or russet
1 yellow onion, thinly sliced
6 large eggs
1 tsp salt plus more to taste
¼ tsp black pepper

Method

Heat the olive oil in a 10-inch nonstick or well-seasoned skillet over medium-low heat. Add the potatoes and onion, season with the salt, and cook gently, turning with a spatula every few minutes, until the potatoes are tender when pierced but not browned.
20 min
Scoop the potatoes and onion into a colander set over a bowl to drain, reserving the oil underneath.
2 min
Whisk the eggs with the pepper in a large bowl. Fold in the warm potatoes and onion and let the mixture sit so the potatoes soak up the egg.
5 min
Wipe out the skillet and add 2 tablespoons of the reserved oil. Heat over medium-high, pour in the potato-egg mixture, and spread it into an even layer. Cook undisturbed, shaking the pan occasionally so it doesn't stick, until the edges are set.
3 min
Cover the pan with a plate larger than the skillet, invert the tortilla onto it, then slide it back into the pan uncooked-side down, tucking the edges in with the spatula. Cook until just set at the center — it should feel like a firm custard, not hard.
3 min
Slide the tortilla onto a plate and let it rest before slicing.
2 min

Substitutions

Russet potatoes — Yukon Golds hold their shape a little better and are less likely to break apart while cooking, but either works fine.
The onion — Some regions of Spain leave it out entirely — a purist's tortilla is just potatoes and eggs. Leave it out if you'd rather, no adjustment needed.
A plainer tortilla — Stir a handful of diced cooked chorizo or roasted red pepper in with the potatoes for a heartier version.

Storing leftovers

Keeps three days in the fridge, covered. It's traditionally eaten at room temperature, so pull it out about 30 minutes before serving; if you want it warm, reheat covered in a low oven or the skillet rather than the microwave, which turns the egg rubbery.

Questions

Why do the potatoes cook in so much oil?

It's essentially a confit — the low, steady oil bath cooks the potatoes through gently so they stay tender instead of browning. Most of the oil gets drained off before the eggs go in.

Can I reuse the oil I drain off?

Yes. Strain it and keep it in the fridge — it picks up flavor from the potatoes and onion and is good for roasting vegetables or frying eggs another day.

Do I really have to flip it?

Flipping is how the tortilla cooks through on both sides without drying out on top. Use a plate a bit larger than the pan, and do it over the sink the first time in case of spills.

How do I know when it's done?

Press the center gently — it should give like a firm-set custard, not feel liquid or feel hard. It will firm up a little more as it rests.