Pat the chicken breasts dry with paper towels and season evenly with 1 teaspoon salt, 1/2 teaspoon black pepper, and 1/2 teaspoon garlic powder.

Heat 2 tablespoons olive oil in a large skillet over medium-high heat until shimmering.

Place the chicken breasts in the skillet and sear without moving for 6 to 7 minutes to form a golden crust.

Flip the chicken breasts and cook for an additional 5 to 6 minutes, or until the internal temperature reaches 165°F (74°C), then transfer to a cutting board and let rest for 5 minutes.

Bring a large pot of salted water to a rolling boil, then add 1 pound fettuccine and cook according to package directions (8 to 10 minutes) until al dente.

Meanwhile, in a medium saucepan over medium heat, melt 4 tablespoons unsalted butter, then add 4 minced garlic cloves and cook for about 30 seconds until fragrant.

Pour in 1 cup heavy cream and 1/2 cup whole milk, stirring constantly and heating until small bubbles appear around the edges without boiling.

Remove the saucepan from heat and stir in 1 cup grated Parmesan cheese a handful at a time, mixing until each addition melts completely.

Season the sauce with 1/4 teaspoon white pepper, 1/4 teaspoon salt, and a pinch of nutmeg, adjusting to taste.

Drain the cooked pasta, reserving 1 cup of pasta water, then toss the pasta in a large mixing bowl with the sauce, adding pasta water by the tablespoon if needed to reach desired consistency.

Slice the rested chicken breasts into strips, divide the sauced pasta among serving plates, top with sliced chicken, sprinkle with 2 tablespoons chopped fresh parsley, and serve with extra Parmesan cheese.