In a 2-quart saucepan, heat the milk on medium heat. In a separate saucepan, melt the butter and stir in the flour. Stir and cook for two minutes. Add the warmed milk, and stir constantly over low heat until smooth and thick. This takes 3 to 5 minutes.
Beat egg yolks with a fork or whisk. Stir a small amount of milk sauce in the egg yolks. Beat together, then pour in remaining milk sauce. Stir in cheese, mustard, fresh herbs, nutmeg, salt, and pepper. Beat the egg whites to soft peaks. Fold half of the beaten egg whites into the sauce. Gently fold in the remaining egg whites.
Put mixture in a well-greased souffle dish. If desired, put a rim of parchment or aluminum foil as a collar around the top of the dish (this must also be greased). Bake at 350 degrees for 45 minutes. Test with knife. Serve immediately.