It took me a while to perfect this one. The most important thing about serving a soufflé is to place it on the table before guests the second it comes out of the oven. Humidity can affect the way your soufflé turns out: the drier, the better. Be sure to beat the egg whites until softly stiff, but not dry. Make sure there is not a trace of grease on the beaters or bowl.
Make white sauce: Stir together butter and flour in a sauce pan over low heat until smooth and well-blended. Over medium heat, gradually stir in milk until smooth, and it just comes to a boil. Remove from heat and cool 1 minute, stirring.
Stir about 2 tablespoons of the white sauce into the beaten egg yolks, to "temper" the yolks and keep them from cooking.
Then, add to the white sauce, stirring well, the cheeses and beaten egg yolks. Cool mixture to room temperature.
While mixture is cooling, beat the egg whites until softly stiff, but not dry. Fold the egg whites into the cheese mixture.
Immediately pour entire mixture into a well-greased and lightly floured soufflé dish. This dish should be round, about 7-8" in diameter, with tall straight sides. Use shortening or butter to grease it with, and lightly dust with real flour. I haven't had much success using Baker's Joy Cake Release or similar products.
Decorate the top of the soufflé with paper-thin slices of Swiss cheese cut into fancy shapes. Bake 25-30 minutes or until set. Serve immediately, before it loses its "pouf".