Cook the pasta in a large pot of salted boiling water according to the package directions until al dente.
Before draining, make sure to reserve about 1 cup of the pasta water. This starchy water is the key to a silky, emulsified sauce that clings beautifully to every strand of pasta.
While the pasta cooks, melt the butter in a large skillet over medium heat. If using garlic, sauté it in the butter for 1–2 minutes until fragrant but not browned.
Pour in the heavy cream and bring it to a gentle simmer. Let it bubble for 3–4 minutes, stirring often. You’re not trying to reduce it too much — just enough to blend with the butter
Lower the heat and slowly whisk in the grated Parmesan cheese. Stir until the cheese melts and the sauce is smooth. Season with salt and pepper to taste.
Add the drained pasta directly to the sauce and toss gently to coat every strand. If the sauce feels too thick, gradually add some of the reserved pasta water, a few tablespoons at a time, until you reach your desired consistency.
Let everything simmer together for just another minute or two to marry the flavors. Then, remove from heat. Plate your fettuccine Alfredo immediately — it’s best eaten hot and fresh.
