Cook the elbow macaroni according to the package instructions.
In a large saucepan, melt the butter over medium heat.
Add the flour and cook for 1 minute, stirring constantly.
Whisk in the milk and bring to a simmer. Cook for 3 minutes, stirring constantly, until thickened.
Remove from the heat and stir in the Parmesan cheese, nutmeg, salt, and pepper.
In a large skillet, cook the bacon, onion, and mushrooms over medium heat until the bacon is crisp and the vegetables are softened, about 5 minutes.
Drain the cooked macaroni and add it to the sauce. Stir to combine. Taste and adjust the seasoning if desired.
Transfer the macaroni to a greased baking dish. Top with the bacon, onion, and mushroom mixture. Bake at 350°F for 20 minutes, or until the top is golden and bubbly.
Serve hot.
Interesting Facts
This dish is a traditional Swiss-Italian dish, often served as a comfort food.
This dish is also known as maccheroni alpina.
Nutmeg is a key flavor in this dish, so be sure to use freshly grated nutmeg for the best flavor.