This is actually a bit of a cross between an omelet and a soufflé. The eggs are separated and the whites are whipped to soft peaks and added to the mixture. This addition causes the omelet to puff up some. The cheese here is variable, fontina is a excellent melting cheese. Other good melters are Gruyère, Emmental, raclette and provolone. However go with what you have on hand or prefer.  Omelets are traditionally folded in half or even thirds while on the stovetop and sometimes even flipped over in the pan and while you could do those here, you may sacrifice some of the puffiness, hence the broiling. You could also cover the pan and let the omelet steam finish. I like the broiling method because it gives the omelet a slightly crusty top.

1/4 c vegetable oil, or 2 T vegetable oil and 2 T butter; divided
4 – 5 c arugula, spinach or other green, chopped
6 eggs, separated
salt and pepper, to taste
(fresh) grated nutmeg, to taste
1 c Fontina cheese, shredded or grated; divided

1. Preheat the broiler, if using, and position a rack 6 inches from the heat source.

2. Melt 2 T of the fat in a skillet. Add the chopped arugula and sauté for a couple of minutes until wilted. (Sturdier greens will take longer to wilt and become tender.) Remove from skillet and drain. Transfer to a bowl and allow to cool.

3. Beat the egg yolks lightly and add to greens in bowl, along with some salt, pepper, a grating of nutmeg, and a third of the cheese.

4. Whisk or beat the egg whites until soft peaks form. Fold into greens mixtures until no streaks of white remain.

5. Heat the remaining 2 T of fat in the skillet. Scrape the contents of the bowl into the skillet. Spread evenly. Cook over medium heat until the bottom is cooked, 3 minutes or so. Sprinkle with the remaining cheese and put under broiler, for another 3 minutes or so, until the cheese has melted and the top is set.

6. Slide the omelet onto a platter, and fold in half if you wish. Cut into wedges and serve.