Bring a large pot of salted water (using 1 tbsp salt) to a rolling boil. While waiting for the water to heat, prepare all your ingredients: slice the chicken breast into 1/2-inch thick strips, thickly slice the mushrooms into 1/4-inch pieces, dice the small onion, and mince the garlic fresh. Chop the parsley and set aside. Once the water boils, add the fettuccine and cook according to package directions until al dente, then drain and set aside. Starting the pasta first ensures it finishes cooking right when your sauce is ready, giving you perfect timing for assembly.

Season the chicken strips with 1/2 tsp salt and 1/4 tsp pepper. Heat 2.5 tbsp olive oil in a large skillet over medium-high heat until shimmering, then add the chicken in a single layer. Cook undisturbed for about 5 minutes until golden brown, then flip and cook another 2-3 minutes until just cooked through. Remove the chicken to a plate—it doesn't need to be fully cooked since it will finish cooking when returned to the sauce later.

In the same skillet, reduce heat to medium and add 1 tbsp olive oil and 2 tbsp butter. Add the diced onion and cook for about 3 minutes until softened and translucent. Add the sliced mushrooms and cook for 5-7 minutes, stirring occasionally, until they release their liquid and begin to brown—this develops deep, savory flavor. Stir in the minced garlic and cook for just 30 seconds until fragrant. I like using Kerrygold butter here because its higher butterfat content creates a richer, more luxurious sauce base.

Pour the 4 cups of half and half into the skillet with the aromatics and mushrooms, stirring to combine. Bring to a gentle simmer over medium heat and cook for 8-10 minutes, stirring occasionally, until the sauce thickens slightly and coats the back of a spoon. Season with 3/4 tsp salt, 1/2 tsp pepper, and 1/8 tsp ground nutmeg. The nutmeg adds a subtle warmth that's classic in Alfredo and brings all the flavors together beautifully.

Return the cooked chicken from Step 2 to the sauce and stir in the chopped parsley. Cook gently for about 1 minute until the chicken is heated through. Add the drained fettuccine from Step 1 and toss everything together until the pasta is evenly coated with the creamy sauce. Let the finished dish rest for 10-15 minutes before serving—this allows the flavors to meld and makes the dish more cohesive. The pasta will continue to absorb sauce during this time, creating a silkier final texture.