01 - Bring a large pot of salted water to a boil. Add pasta and cook until al dente, following package instructions. Drain and reserve 1/2 cup of pasta water.
02 - Butterfly the chicken breasts and season both sides evenly with salt, pepper, and dried Italian herbs if using.
03 - Heat olive oil in a large skillet over medium-high heat. Sear chicken until golden brown and cooked through, approximately 5–6 minutes per side. Transfer to a plate, cover loosely, and let rest.
04 - Reduce skillet heat to medium. Add butter, followed by onion, and sauté for 2–3 minutes until softened. Add garlic and cook for 1 minute until fragrant.
05 - Pour in chicken broth, scraping up any browned bits from the skillet to incorporate added flavor.
06 - Add heavy cream and bring to a gentle simmer. Stir in Parmesan cheese until the sauce becomes smooth and creamy. Adjust seasoning with additional salt and pepper to taste.
07 - Thinly slice chicken breasts. Return chicken and cooked pasta to the skillet, tossing to combine and heating through. Add reserved pasta water a splash at a time until sauce reaches desired consistency.
08 - Stir in chopped parsley. Serve immediately, garnished with extra parsley and freshly grated Parmesan cheese.