These slow-cooked eggs are typical of Sephardic cooking. They are often simmered in a stew but they can also be cooked separately. The slow cooking makes them especially delicious, and they are an excellent picnic food. The onion skins are the papery brown coverings of yellow onions, not the white inner layers. Eggs can also be cooked in oil and Turkish coffee grounds, which will give them a similar delicious flavor and attractive color.