-and thinly sliced From "Fields of Greens" by Annie Somerville (Bantam Books, 1993, $26.95) First, reduce balsamic vinegar by half in a saucepan over high heat. Set aside. Heat 1 tablespoon of olive oil in a large skillet; add onion, half teaspoon of salt and a few pinches of pepper. Saute onion over medium heat until it begins to release its juices, about 4-5 minutes. Add peppers, garlic and bay leaf; cover and cook very slowly over low heat for about 15 minutes. Set vegetables aside. Remove bay leaf. Preheat oven to 325'F. Beat eggs in a bowl and add onion-pepper mixture, cheeses and basil. Season with remaining quarter teaspoon salt and a few more pinches of pepper. In a 23 cm saute pan with an ovenproof handle, heat remaining tablespoon of olive oil to just below smoking point. Swirl oil around sides of pan to coat it. Turn heat down to low, then immediately pour frittata mixture into pan. Cook frittata over low heat for 1-2 minutes, until sides begin to set; transfer to a 325'F. oven and bake, uncovered, for 20-25 minutes, until frittata is golden and firm. Loosen frittata with a spatula. Place a plate over pan, flip over, and turn frittata out. Brush bottom and sides with reduced balsamic vinegar and cut into wedges.