Bring a large pot of salted water to a boil. Add the pasta and cook until al dente, about 8 to 10 minutes. Reserve 1 cup of pasta water, then drain and set aside.

Heat 2 tablespoons of butter in a skillet over medium heat. Season the chicken with salt and pepper, then add it to the skillet. Cook until golden and cooked through, about 6 to 8 minutes. Transfer the chicken to a plate.

In the same skillet, add the remaining 2 tablespoons of butter. Add minced garlic and diced onion, sautéing until fragrant and translucent, about 3 to 4 minutes.

Pour in the heavy cream and chicken broth. Stir in the Italian seasoning and red pepper flakes. Simmer until the sauce thickens, about 4 to 6 minutes. If it’s too thick, loosen it with the reserved pasta water.

Return the chicken to the skillet, add the drained pasta, and toss to coat well. Let everything heat together for 1 to 2 minutes.

Sprinkle the Parmesan over the pasta, allowing it to melt, then garnish with fresh parsley as desired.