The quantity of vegetable to egg varies enormously, depending upon which kind of vegetable you are using. The basic rule of thumb is that there has to be enough egg to hold the whole dish together, but there must be enough vegetable content for the vegetable to form the main part of the finished dish. I tend to use about two thirds vegetable and one third eggs. Be very careful not to add too much cheese, as this will cause the frittata to stick and make it impossible to turn over successfully. The amount of time it takes to cook the frittata will depend on how thick it is and what kind of pan you are using.
6–10ozvegetable of your choice, such as Swiss chard, spinach, zucchini, or onions (boiled, steamed, or sautéed, then carefully drained of any liquid)
Whatever vegetable you choose to put into the frittata, it must be as dry as possible. This makes the frittata easy to slice into wedges once cooked.
If using green leaf vegetables such as Swiss chard or spinach, squeeze the water out of the cooked leaves before finely chopping. Other vegetables need to be thoroughly drained of any liquid.
Mix the hot or cold vegetable into the beaten eggs, then add the Parmigiano and salt and pepper to taste. Mix well.
Heat the olive oil in a wide, shallow skillet until very hot, then pour in the egg mixture.
Shake the skillet to flatten and even out the frittata, pulling the liquid egg into the center as you work. Cook until the underside is browned and firm.
Turn the frittata over by placing a large plate or lid on top of the skillet and turning the skillet upside down so that the frittata falls onto the plate with the cooked side uppermost.
Carefully slide the frittata back into the hot skillet with the cooked side on top and the uncooked side underneath. Cook until golden brown and firm on the underside. Slide out onto a clean, flat platter and serve hot or cold.