Preheat your oven to 375°F (190°C). Grease a 9x13-inch baking dish with butter or cooking spray.

Cook the elbow macaroni according to the package instructions until al dente. Drain and set aside.

In a large saucepan, melt the butter over medium heat. Once melted, whisk in the flour and cook for about 2 minutes until it turns golden brown and smells nutty.

Gradually pour in the milk while whisking constantly to prevent lumps from forming. Cook the mixture for about 5 minutes until it thickens enough to coat the back of a spoon.

Remove the saucepan from the heat and stir in the salt, black pepper, nutmeg, and half of the grated Gruyère and Emmental cheeses until melted and well combined.

Add the cooked macaroni to the cheese sauce and stir until evenly coated.

Transfer the macaroni and cheese mixture to the prepared baking dish. Sprinkle the remaining Gruyère, Emmental, and Parmesan cheeses evenly over the top.

Bake in the preheated oven for about 25-30 minutes, or until the top is golden brown and the cheese is bubbly and melted.

Once baked, remove the dish from the oven and let it cool for a few minutes before serving.

Serve the macaroni au gratin hot as a delicious main dish or side. Enjoy!