Boil salted water and cook the pasta until al dente; drain and set aside.
In a saucepan, melt butter over medium heat.
Add flour and stir to create a roux.
Gradually whisk in milk, stirring until the sauce thickens.
Season with salt, pepper, and nutmeg.
Stir in grated Parmesan cheese until melted.
Add the cooked pasta to the sauce and mix well.
Incorporate any cooked vegetables or proteins if desired.
Serve immediately, garnished with additional cheese.