Given how successful a Spanish tortilla is served as a panino, we thought we'd try it with another open-faced omelet: the Italian frittata. No surprises here-it works beautifully, too. In fact, when it comes to the perfect example of room-temperature food, there may be no better example than the frittata. Serve it as suggested below or in larger pieces for a superb brunch, late-morning breakfast, or late-evening snack.

A preparation note: While there are few ways to use leftover roasted potatoes that we can recommend, this recipe happens to be an exception. They work deliciously here.