Bring a large pot of salted water to a boil.
Add the fettuccine and cook according to package instructions until al dente.
Melt the butter in a large skillet over medium heat.
Pour in the heavy cream and bring to a simmer, stirring occasionally.
Gradually whisk in the grated Parmesan cheese until melted and smooth.
Season the sauce with salt and pepper to taste.
Drain the cooked pasta, reserving a little pasta water.
Add the fettuccine to the sauce, tossing to coat.
If the sauce is too thick, add reserved pasta water a little at a time.
Serve hot, garnished with fresh parsley.