This is the Genoese omelette. Chop finely one onion and fry it in a mixture of oil and butter; boil in salt water a few leaves of spinach, beetroot greens, young tender artichokes, or any suitable vegetable of that type; when cooked chop them and add them together with the fried onion, to the beaten eggs with a little marjoram, salt and pepper, and grated Parmesan.
There should be a good deal of the chopped vegetables, so that the finished frittata is more green than yellow. Cook on a moderate fire in a frying-pan till the whole thing is set. Do not fold it.