[synaesthetic]

@Aohige: Your white sauce (which is actually bechamel sauce) used to make the basis of this dish (and many others) will taste far better if you make certain to cook the flour in the fat a bit before mixing your cold milk into it. This takes out the "raw flour" taste which can make things quite mealy. The microwave won't cook it properly--the roux needs to very slightly brown in a pan (and I mean VERY slightly, caramelizing a roux is only acceptable if you're going to make gumbo) on the stove or it will retain that raw taste.

Adding a small amount of freshly-ground nutmeg to the finished bechamel sauce also makes a tremendous difference in the flavor, even if you add cheese or garlic or spices to the sauce to flavor it.

Personally when I make any sort of "cheese sauce" for any application, be it cheese dip for tortilla chips or sauce for pasta, rice, or even Southern-style macaroni & cheese, I never use a bechamel sauce. I find that even with cookking the roux thoroughly it still retains a very mealy flavor that I find objectionable. I take the much richer (but much more fattening) route of mixing one part heavy cream with one part whole milk in a saucepot on the stove. Season this with salt and pepper (use white pepper if you don't like the black flecks) and slowly bring it up to temperature. Don't let it boil or you risk "breaking" the dairy, especially once the cheese is added. Slowly add grated cheese of your choice and stir until it melts completely. If you don't want the sauce to be too gloopy and treacly, add a small amount of lime juice (about a teaspoon). The citric acid will cut the proteins slightly and prevent them from tangling around each other and becoming very stringy--this is critical if you melt in cheeses like mozzarella.