01 - Bring a large pot of salted water to a rolling boil. Add the pasta and cook according to package directions until al dente. Reserve ½ cup of the starchy pasta water before draining. Set the drained pasta aside.
02 - While the pasta cooks, season the sliced chicken breasts generously with salt and freshly ground black pepper on both sides.
03 - Heat olive oil in a large skillet over medium-high heat. Add the seasoned chicken slices in a single layer and cook for 4 to 5 minutes per side until deeply golden and cooked through. Transfer the chicken to a plate and keep warm.
04 - In the same skillet, melt the butter over medium heat. Add the chopped onion and sauté for about 2 minutes until softened and translucent. Add the minced garlic and cook for an additional minute until fragrant, stirring constantly to prevent burning.
05 - Reduce the heat to medium-low. Pour in the heavy cream and whole milk, stirring to combine. Bring the mixture to a gentle simmer—do not boil. Gradually whisk in the freshly grated Parmesan cheese, allowing each addition to melt smoothly before adding more. If the sauce is too thick, thin it with the reserved pasta water, one tablespoon at a time, until the desired consistency is reached. Sprinkle in the dried Italian herbs if using.
06 - Add the drained pasta and seared chicken back into the skillet with the sauce. Toss everything together until the pasta and chicken are evenly coated. Taste and adjust the seasoning with additional salt and pepper as needed.
07 - Divide among serving plates or bowls immediately while hot. Garnish with freshly chopped parsley and an extra shower of grated Parmesan cheese if desired. Serve alongside crusty bread or a simple green salad.