The primary ingredient in a traditional Spanish tortilla is eggs. The dish, also known as tortilla Española, typically consists of a mixture of beaten eggs and sliced or diced potatoes, which are cooked together in a frying pan until set. Some variations may include onions for added flavor, but the core elements remain the eggs and potatoes. This dish is a staple in Spanish cuisine and can be served hot or cold, often as a tapas dish or a primary meal. The simplicity of its ingredients belies the technique required to make it perfectly fluffy and flavorful.