Bring a large pot of salted water to a boil and cook the fettuccine until al dente. Reserve 1/2 cup pasta water, then drain.
Melt the butter in a large skillet over medium heat. Add garlic and cook for 1 minute until fragrant.
Pour in the heavy cream and simmer gently.
Reduce heat to low and whisk in parmesan a handful at a time until melted and smooth.
Season with salt, pepper, and nutmeg.
Add the drained fettuccine to the skillet and toss to coat, adding reserved pasta water as needed to adjust consistency.
Garnish with parsley and extra parmesan, then serve immediately.
