Both Spanish omelets and American omelets use beaten eggs as a base. In the United States, the eggs are usually cooked on their own without stirring before being folded over the fillings, which can include meats, cheeses, vegetables, herbs, and more. A Spanish omelet, on the other hand, is made with fried potatoes (and occasionally caramelized onions) that are incorporated directly into the beaten egg mixture to cook the finished omelet.