Frittata di Cipolle

A frittata is something like an open-faced omelet; a thin round of egg is cooked in butter or oil until the egg is softly set but not runny, and the top of the frittata is nicely browned. Frittate are tremendously versatile: They are flavored with herbs and bolstered with cooked vegetables, cheese, meats, seafood, and pasta, any of which may be stirred into the beaten raw egg before the frittata is cooked. Frittate are cooked over medium–low heat to prevent the eggs from tough