Begin by bringing a large pot of salted water to a boil. Add the dry fettuccine or pasta of your choice, and cook according to package instructions until al dente. Before draining, reserve 2 cups of the pasta cooking water for later use. Drain the pasta and set it aside.
In a large skillet over medium heat, melt the cubed unsalted butter. Allow it to melt completely, stirring occasionally to prevent browning.
Once the butter has melted, gradually add 1 cup of the reserved pasta cooking water to the skillet. Whisk the mixture until combined. This step creates a light, creamy base for your Alfredo sauce.
Lower the heat and slowly add the finely grated Parmesan cheese to the skillet. Stir continuously with the whisk until the cheese is fully melted and the sauce is smooth. If the sauce is too thick, you can add a bit more reserved pasta water to achieve your desired consistency.
Season the sauce with kosher salt and freshly ground black pepper to taste. Add the sliced cooked chicken breasts to the skillet, gently tossing them in the sauce until well coated.
Add the cooked fettuccine to the skillet, tossing everything together until the pasta is well coated in the Alfredo sauce. If needed, add more pasta water to keep the sauce silky and smooth.
Serve your Alfredo pasta immediately, garnishing with additional Parmesan cheese and chopped fresh parsley or basil leaves if desired. Enjoy the creamy goodness without the heaviness!