For 4 people, you gently stew two medium-sized red peppers (or green if you like) and an onion, each thinly sliced from top to bottom, in some olive oil until they are quite soft. This will take anywhere between 20 and 30 minutes (or even more, if you want them very soft). Regulate the heat so that the vegetables only slightly brown, if at all. Season with salt and pepper, and allow them to cool, covered, for a few minutes. (This rest under cover will further soften the vegetables and, for some mysterious reason, tends to enhance their flavor.) Then mix the vegetables with six eggs, some grated cheese and a pinch of salt, and proceed as for any frittata.
NOTES: As with peperonata, you can convert this into a more substantial dish by frying some sausage along with the peppers and onions, either sliced or crumbled. Some cubed pancetta might also be nice, though I haven’t tried it. And if you want a really substantial dish, add some cubed potatoes to the mix.
You should slice both peppers and onions vertically, from top to bottom. The onions, in particular, need to be sliced in this way in order to retain their shape; sliced horizontally, onions will simply ‘melt’ away, something you don’t necessarily want for this dish.