Like whole egg omelets, those made with the whites alone dry out when they cook for too long at too high a heat. Or they can get rubbery if you don't whisk them long enough to break them up. A wet omelet can be caused by one of three things—adding too much liquid to the whites (you don't need any), using wet fillings (raw tomatoes or soggy spinach) or undercooking.
Tina Ujlaki called Capton Place chef Laurent Manrique and he gave her his fail–safe method. He has two secrets—first he beats a little melted butter into the egg whites before they go into the pan, and when the omelet is almost set, he runs it under the broiler to set the top without overcooking the bottom. If you're concerned about calories or cholesterol, omit secret number one but follow Manrique's broiler method.
1/2 cup small chanterelles or sliced wild mushrooms
Salt and freshly ground pepper
4 large egg whites
Preheat the broiler; set a rack 5 inches from the heat. Heat 1 tablespoon of the butter in a medium nonstick ovenproof skillet. Add the shallot and thyme and cook over moderate heat, stirring, until fragrant, about 30 seconds. Add the mushrooms, season with salt and pepper and cook over moderately high heat until tender and lightly browned, about 5 minutes.
In a medium bowl, whisk the egg whites until frothy. Season with salt and pepper and beat in the remaining 1 tablespoon of melted butter. Pour the beaten whites into the skillet and cook over moderate heat until almost opaque, drawing in the edges of the omelet with a spatula as they set and tilting the pan to allow the uncooked whites to seep underneath, about 40 seconds.
Transfer the skillet to the oven and broil the omelet for about 10 seconds, or until the top is just set. Run the spatula around the edge of the omelet to release it. Fold one third of the omelet onto itself, then roll it out onto a plate in a neat shape and serve at once.