Heat a 17 centimeter nonstick skillet over medium low, arrange your top oven rack about 15-20 centimeters below your broiler, and turn the broiler on to high.
Meanwhile, separate your eggs by placing the yolks in a medium bowl and the whites into a very clean large metal or glass bowl. When separating your eggs, it is important to make sure that no yolk gets into your whites. Even the littlest bit of yolk or fat can stop your whites from whipping up.
Using a clean metal whisk or hand mixer, whip up the egg whites until they are fluffy and hold soft peaks. Set those aside and whisk up the egg yolks with a bit of salt. The yolks need to be whisked for about ten seconds or so, just until they lighten up a bit.
Using a metal spoon or large whisk, gently fold the yolks into the whites just until combined. The mixture will fall a bit and lose some of its fluffiness but be careful not to over stir as this will ruin the soufflé.
Pop the butter into your preheated pan, swirl around a bit so that the bottom and edges are nicely coated, and gently pour the egg mixture into the pan.
Cook the omelette over medium low heat for one minute, gently sprinkle the cheeses on top, and pop the pan under the broiler for three to four minutes or until the cheese just begins to turn golden.
Remove the omelette from the oven and carefully fold it over on itself and transfer to a plate. Top with a scattering of chives and a bit more salt and pepper, if desired.