Bring a large pot of salted water to a boil and cook the fettuccine pasta according to the package directions until al dente. Before draining, scoop out about 1/4 cup of the pasta cooking water and set it aside, then drain the pasta.

While the pasta cooks, pat the boneless skinless chicken breasts dry with paper towels, then season both sides with about half of the salt and half of the black pepper.

Heat the olive oil in a large skillet over medium-high heat. Add the seasoned chicken breasts and cook for about 5 to 7 minutes per side, or until golden on the outside and cooked through in the center.

Transfer the cooked chicken to a cutting board and let it rest for a few minutes, then slice it into thin strips or bite-sized pieces and set aside.

In the same skillet, reduce the heat to medium and add the unsalted butter. Once the butter has melted, add the minced garlic and cook, stirring frequently, for about 30 seconds to 1 minute, just until fragrant but not browned.

Pour in the heavy cream, stirring to combine with the butter and garlic, and bring the mixture to a gentle simmer over medium heat.

Stir in the freshly grated Parmesan cheese a handful at a time, whisking until the cheese melts smoothly into the cream and the sauce thickens slightly.

Season the Alfredo sauce with the remaining salt and black pepper, tasting and adjusting if needed so the flavor is balanced and well seasoned.

Add the drained fettuccine pasta directly into the skillet with the Alfredo sauce and toss gently to coat the pasta evenly, using a bit of the reserved pasta cooking water to loosen the sauce if it seems too thick.

Add the sliced cooked chicken to the skillet and toss again so the chicken is coated in the sauce and warmed through, adding a splash more pasta water if you prefer a looser sauce.

Sprinkle the chopped fresh parsley over the Chicken Alfredo, give everything a final gentle toss, and serve hot with extra Parmesan cheese on top if desired.