Bring a large pot of salted water to a boil. Cook the pasta according to the package directions until al dente.
Scoop out ½ cup of the pasta water and set it aside, then drain the pasta.
Return the empty pot to medium-low heat and melt the butter. Add the garlic and cook for 1 minute, stirring, until fragrant but not browned.
Add the pasta, Parmesan and ¼ cup of the reserved pasta water. Toss for 1–2 minutes, until the sauce is glossy and coats the noodles. Add more pasta water a splash at a time if it looks dry.
Season with the salt and pepper, sprinkle with parsley and serve with extra Parmesan.