Fill a large pot with water, salt it well, and bring to a rolling boil. Add the fettuccine and cook until just shy of al dente per package directions. Reserve about 1 cup of the pasta water, then drain.

While the pasta cooks, pat chicken dry and season both sides with 1 teaspoon of the kosher salt, black pepper, and garlic powder if using.

Heat a large skillet over medium-high. Add olive oil until shimmering. Add chicken and sear 4–6 minutes per side, until golden and cooked through (internal temp 165°F/74°C). Transfer to a plate and rest 5 minutes, then slice into strips.

Reduce heat to medium. In the same skillet, add butter and let it melt. Add minced garlic and sauté 30–45 seconds until fragrant—do not let it brown.

Pour in the heavy cream and bring to a gentle simmer. Stir in nutmeg and the remaining 1/2 teaspoon salt. Let bubble lightly for 2–3 minutes to thicken slightly.

Lower heat to medium-low. Add the Parmesan in small handfuls, stirring until completely smooth and glossy. If the sauce gets too thick, add a splash of reserved pasta water to loosen.

Add the drained fettuccine to the skillet and toss to coat. Add pasta water a little at a time until the sauce lightly clings to the noodles. Fold in the sliced chicken and any resting juices.

Adjust salt and pepper. Squeeze a little lemon over the top if you want brightness. Garnish with chopped parsley and extra Parmesan.

Serve immediately. Alfredo is best hot from the stove when the sauce is silky and glossy.