How to Make It
Preheat the broiler and adjust a rack so that the top of the skillet will be about 6 inches from the heat. In a 10- to 12-inch ovenproof skillet, heat 2 tablespoons of the olive oil. Add the onion and cook over moderately low heat until softened but not browned, 6 to 8 minutes. Scrape the onion into a small bowl, add the mint and let cool completely.
In a medium bowl, combine the eggs, cheese and the cooled onion-mint mixture. Season with salt and pepper.
Return the skillet to moderately high heat and add the remaining 1 tablespoon oil. Swirl the pan to coat the bottom and sides with the oil. Add the beaten eggs and cook, occasionally lifting the set sides to allow the uncooked eggs to seep underneath, until the bottom is golden and set, 5 to 7 minutes.
Place the frittata under the broiler for about 30 seconds to cook and brown the top. Cut into wedges or small squares and serve hot, warm or at room temperature.