Bring a large pot of salted water to a rolling boil. Cook pasta until al dente per package directions. Reserve ½ cup pasta water; drain.

Pat chicken dry. Season with salt, pepper, and ½ tsp Italian seasoning. In a large skillet over medium-high heat, melt 1 Tbsp butter. Sear chicken 3–4 minutes per side until golden and cooked through. Transfer to a plate, keeping the juices.

Lower heat to medium. Add remaining 2 Tbsp butter. Stir in garlic and red pepper flakes; cook for 30–60 seconds until fragrant.

Pour in chicken broth, scraping browned bits. Stir in heavy cream and remaining ½ tsp Italian seasoning. Simmer gently for 2–3 minutes until slightly thickened.

Reduce heat to low. Gradually sprinkle in Parmesan, stirring until fully melted and the sauce is velvety smooth.

Return chicken (and juices) to the skillet. Add drained pasta. Toss until evenly coated. If the sauce is thick, stir in splashes of reserved pasta water until glossy and clinging to the pasta.

Taste and adjust salt and pepper. Garnish with chopped parsley and serve immediately.