01 - Bring a large pot of salted water to a rolling boil. Add pasta and cook according to package directions until al dente. Reserve ½ cup of pasta water before draining. Set drained pasta aside.
02 - While the pasta cooks, season the thinly 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 golden brown 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. Stir in the minced garlic and cook for 1 minute until fragrant, being careful not to burn it.
05 - Reduce heat to medium-low. Pour in the heavy cream and whole milk, stirring to combine. Bring the mixture to a gentle simmer. Gradually whisk in the freshly grated Parmesan cheese until fully melted and the sauce is smooth and velvety. If the sauce is too thick, thin it with small amounts of the reserved pasta water until the desired consistency is reached. Sprinkle in the dried Italian herbs if using.
06 - Add the drained pasta and seared chicken to the skillet with the cream sauce. Toss everything together until the pasta and chicken are evenly coated. Taste and adjust seasoning with additional salt and pepper as needed.
07 - Divide among plates and serve immediately. Garnish with freshly chopped parsley and an extra shower of grated Parmesan if desired.