Brush a
gratin dish with a half tablespoon of
butter. Drain the macaroni, discarding the aromatics, and return the drained macaroni to the same saucepan. Add the
sauce along with the Gruyère and half the
Parmesan to the macaroni and mix well.
Place the macaroni mixture in the
gratin dish and level the top. Sprinkle the remaining
cheese over the top. Dot the top with the remaining
butter.