Preheat your oven to 360°F (180°C) and lightly grease a 12-inch round baking dish or medium casserole dish.
In a large bowl, mix all the shredded cheeses together, then set aside about a quarter of it for topping later.
Bring a large pot of salted water to a boil, cook the macaroni until just al dente (1 to 2 minutes less than the package says), then drain and set aside.
In another large pot, melt the butter over medium-low heat, then whisk in the flour and cook for about 2 minutes while whisking constantly.
Slowly pour in the milk while whisking to keep the sauce smooth, then continue stirring for 5 to 6 minutes until it thickens slightly.
Stir in the cheese blend a handful at a time, letting it melt before adding more, then season the sauce with salt, pepper, and nutmeg.
Add the cooked macaroni to the cheese sauce and stir until all the pasta is evenly coated.
Pour the mac and cheese into your prepared baking dish, then sprinkle the top with the remaining cheese and any optional toppings.
Bake uncovered for 20 to 25 minutes until the top is golden and bubbly, and broil for 1 to 2 minutes if you want a crispier finish.
Let it rest for 5 minutes out of the oven before serving it up hot and melty.