01 - Bring a large pot of salted water to a boil. Add pasta and cook according to package instructions until al dente. Drain, reserving 1/2 cup of pasta water.
02 - While pasta cooks, butterfly chicken breasts and season both sides with salt, pepper, and Italian herbs if desired.
03 - Heat olive oil in a large skillet over medium-high heat. Sear chicken breasts until golden brown and fully cooked, approximately 5 to 6 minutes per side. Transfer to a plate, cover loosely, and let rest.
04 - Using the same skillet, reduce to medium heat. Melt butter, then add chopped onion; sauté for 2 to 3 minutes until softened. Add minced garlic and cook until fragrant, about 1 minute.
05 - Pour in chicken broth and deglaze skillet, scraping up any browned bits from the bottom.
06 - Add heavy cream and bring to a gentle simmer. Stir in grated Parmesan cheese until sauce is smooth and creamy. Adjust seasoning with additional salt and pepper if needed.
07 - Slice chicken breasts thinly. Add sliced chicken and cooked pasta to the skillet. Toss together, incorporating some reserved pasta water as necessary to achieve a creamy consistency.
08 - Stir in chopped parsley and serve immediately, garnished with extra parsley and Parmesan if desired.