01 - Fill a large pot with salted water and bring to a boil. Add pasta and cook until al dente following package instructions. Reserve 1/2 cup of pasta water before draining.
02 - Butterfly chicken breasts and season both sides generously with salt, black pepper, and dried Italian herbs if desired.
03 - Heat olive oil in a large skillet over medium-high heat. Sear chicken on both sides until golden and fully cooked, 5 to 6 minutes per side. Remove chicken from skillet, cover loosely, and let rest.
04 - In the same skillet, reduce heat to medium, add butter, and sauté chopped onion for 2 to 3 minutes until softened. Add minced garlic and cook until fragrant, about 1 minute.
05 - Deglaze skillet with chicken broth, scraping up browned bits. Pour in heavy cream, bring to a gentle simmer, and stir in Parmesan cheese. Mix until smooth and creamy; adjust seasoning with additional salt and pepper.
06 - Slice rested chicken breasts thinly. Return sliced chicken and cooked pasta to the skillet. Toss thoroughly, incorporating reserved pasta water as needed for a silky sauce.
07 - Stir in chopped parsley. Serve immediately, garnished with extra parsley and additional Parmesan if desired.