Separate the eggs. Begin by separating the eggs. Place the egg whites in a very clean metal mixing bowl, and the egg yolks in a small bowl. Allow the eggs to come to room temperature for about 20 minutes.
Prep work. Preheat the oven to 400°F (200°C). Shred the cheese if necessary. In the microwave, melt a teaspoon of butter in a two quart souffle dish. Use a pastry brush to thoroughly coat the sides and bottom of the dish with melted butter.
Make the bechamel. Melt the butter in a medium sized sauce pan on medium heat. When it is melted, stir in the flour with a wooden spoon. Cook, stirring frequently, for two minutes or until the mixture is foamy. Add the milk, slowly at first and stirring after each addition to keep lumps from forming. After you've added about half the milk, you can just pour in the rest.
Add cheese, cool, add egg yolks. Heat the sauce for several minutes until it is thickened and almost boiling. Lower the heat and stir in nutmeg and season to taste with salt and pepper. Stir in the cheese, adding a bit at a time and stirring until blended after each addition. Remove from heat and allow to cool for 10 minutes. After 10 minutes, mix in the egg yolks.
Beat the egg whites. Using an electric whisk, beat the egg whites with the cream of tartar until they are stiff and glossy.
Fold in the egg whites. Blend 1/4 of the egg whites into the cheese sauce to lighten it for the folding process. Place the rest of the egg whites on top of the lightened sauce and use a rubber spatula to cut in the egg whites and fold over the sauce. Turn the pan a little and continue cutting, folding and turning until the egg whites are blended with the sauce. Don't over blend, about a minute should do it.
Bake. Pour the batter into the prepared souffle dish and place the dish in the preheated (400°F - 200°C) oven. Bake for 30 minutes - no peeking. Remove from the oven and serve immediately.
You can also make this recipe in individual ramekins. It makes enough for 6 serving sized ramekins. Reduce the baking time to 18 minutes.
You can prepare the bechamel sauce in advance, just make sure it is at room temperature when you fold in the egg whites.