Bring a large pot of water to a boil and season it generously with salt. Cook the fettuccine until al dente, according to the package instructions. Before draining, reserve about 1 cup of the pasta water, then drain the pasta.
While the pasta cooks, place a wide pan over medium-low heat and melt the butter gently. Once melted, add the grated garlic and heavy cream. Stir to combine, allowing it to warm through and come to a gentle simmer.
Add half of the grated Parmesan to the cream and stir continuously until fully melted and smooth. Let the sauce simmer gently for 2–3 minutes to slightly thicken and develop flavor.
Add the drained fettuccine directly into the pan and toss gently so the pasta is evenly coated in the sauce.
Lower the heat and add the remaining Parmesan gradually, tossing continuously to create a smooth, creamy texture.
Adjust the consistency with a splash of reserved pasta water if needed, until the sauce becomes silky and coats the pasta perfectly.
Season with freshly ground black pepper and taste, adjusting with a little salt if needed.
Serve immediately, finished with extra Parmesan and black pepper, while the sauce is at its best—smooth, glossy, and creamy.