Method
- Pat the chicken pieces dry and season with half the salt (1/2 teaspoon) and half the pepper (1/4 teaspoon).
- Heat the olive oil in a large, deep skillet or wide pot over medium-high heat until shimmering. Add the chicken in a single layer, without crowding, and cook undisturbed for 3 to 4 minutes until golden brown on the bottom.
- Flip the pieces and cook another 3 minutes, until an instant-read thermometer reads 165 F in the thickest piece and no pink remains inside when you cut one open. Transfer the chicken to a plate and set aside; it will finish cooking a bit more later in the sauce.
- Lower the heat to medium and melt the butter in the same pot, scraping up any browned bits from the chicken as it melts. Add the garlic and cook for 30 seconds, stirring constantly, until fragrant but not browned.
- Pour in the chicken broth and bring to a boil over medium-high heat, then add the fettuccine, breaking the strands in half if needed to fit in the pot. Push the pasta down so it's mostly submerged.
- Reduce the heat to medium so the liquid is at a steady simmer, and cook, stirring frequently with tongs to prevent sticking, for 10 to 12 minutes, until the pasta is almost tender (taste a strand; it should have just a slight bite left) and most of the liquid has been absorbed.
- Stir frequently during this stage, especially in the last few minutes, since the starchy liquid thickens quickly and can scorch on the bottom if left unstirred.
- Pour in the heavy cream and stir to combine, then reduce the heat to low. Let the sauce simmer gently for 2 to 3 minutes until it thickens slightly and coats the pasta.
- Remove the pot from the heat and stir in the Parmesan cheese a handful at a time, mixing well after each addition until fully melted and smooth; adding it off direct heat and gradually prevents the cheese from clumping or turning grainy.
- Return the chicken and any accumulated juices to the pot and stir to combine, letting everything sit for 1 to 2 minutes so the chicken reheats through.
- Season with the remaining 1/2 teaspoon salt, 1/4 teaspoon pepper, and the nutmeg if using, tasting and adjusting as needed; the sauce should taste rich and well-seasoned, not flat.
- Garnish with chopped parsley and serve immediately while the sauce is still glossy and warm, since Alfredo thickens further as it cools.
Tips
Stir the pasta frequently while it cooks in the broth, since the starch released makes the sauce thick enough to scorch if left alone.
Add the Parmesan off the heat in small handfuls rather than all at once to keep the sauce silky instead of clumpy.