When I first went to live in Spain in the 1970s, I ate eggs almost every night for supper. I wasn’t alone. Rain or shine, in every season, as night fell, the clatter of forks beating eggs for tortilla de patata (potato omelet) would ring through my neighborhood. As soon as the clanging began to fade, I could hear the hiss of onions and potatoes being sautéed in olive oil, followed by waves of delicious aroma wafting through the air.

Spaniards eat tortilla de patatas at all hours of the day, hot from the pan for supper or lunch, at room temperature as a midmorning snack, or washed down with a glass of wine at a tapas bar. For long car trips and picnics, this is the food they are most likely to bring along—something portable and filling that they can eat without fuss. To this day I think of it as comfort food for all seasons.

There is nothing quaint or fluffy about a tortilla de patatas. Shaped like a round cake because it takes the form of the frying pan it is cooked in, the Spanish tortilla is a sturdy and substantial egg, onion, and potato dish—a type of frittata. In my student days at Valladolid, I would go to a small bar not far from the university for a slice of the largest tortilla I had ever seen. What I loved the most was its spiciness because it was flavored with guindillas, Spain’s favorite hot pepper.

Making a great tortilla de patatas takes a bit of practice, as you need to flip the tortilla to cook it on both sides. It also requires a grassy olive oil and the freshest, most flavorful eggs you can find. I always look for free-range, organic eggs with bright golden-orange yolks. (You can always tell when an egg is fresh because the yolk is dome-shaped, never flat.) Don’t be stingy with the oil when sautéing the onions and potatoes. Once the potatoes are tender and the onion has cooked down to the consistency of a confit, you drain off the oil and reserve it to flavor and cook the eggs. Some Spanish cooks I know claim that extra-virgin olive oil darkens the tortilla. They prefer to use sunflower oil, but I can’t do without olive oil. Use a heavy-bottomed, well-cured or nonstick skillet and a gentle heat as high heat can result in a burnt crust and a runny interior.

My recipe is heavy on potatoes and roasted peppers, but you can reduce the amount for an eggier omelet. Bring it to the table on a platter with warm crusty bread, Romesco Sauce, and a crisp red wine from La Rioja or Ribero del Duero region for a rustic supper or lunch. To serve the omelet as tapas, cut into small squares and serve with romesco as a dipping sauce.