While the macaroni and cheese is boiling, heat the olive oil in a large skillet over medium high heat.
Add the onion and salt and stir occasionally till the onions start to turn brown and caramelize.
Add the beef broth and thyme, and cook until the broth is absorbed. Top your bowl of prepared mac and cheese with some of the onion mixture, sprinkle with a little swiss cheese and crushed croutons.