The key to this is the cheese sauce.
Dont bother mucking about with a roux if you want something unctuous and silky and full of flavour
You get single cream, you get grated cheese of a number of flavours if you wish, nice and strong, nice and deep, you then warm the cream in a pan, add in the grated cheese slowly, stir stir stir, the cheese should melt into the cream without lumps because of the way fat melts together. Add a bit of milk if its too thick. Add white pepper (much better flavour), english mustard, bit of nutmeg if you are so inclined. Nice and powerful
Ive used this with a number of different types of cheese, my best combination was a bit of mild blue, gouda or edam (need to be careful with that due to the poor melting ability), strong cheddar and then ricotta (can get a bit grainy so get a smooth one).
Others have involved a lot of pecorino, and I mean a lot
I havent had it for years due to dieting etc. Its amazing though
You can then add whatever other flavours to the actual macaroni like others have said above, personally I like it nice and simple