Bring a large pot of generously salted water to a rolling boil. Add your pasta and cook according to package directions until al dente, usually 8 to 10 minutes. Before draining, use a ladle or measuring cup to scoop out about ½ cup of the starchy pasta water and set it aside, then drain the pasta in a colander.

While the pasta cooks, pat the chicken cubes completely dry with paper towels and season them generously with salt, pepper, and half of the Italian seasoning.

Heat 1 tablespoon of butter in a large 12-inch skillet over medium-high heat. Once the butter is shimmering and fragrant, add the chicken in a single layer. Let it sear undisturbed for 3 to 4 minutes until golden brown, then flip and cook another 3 to 4 minutes until cooked through and internal temperature reaches 165°F. Remove chicken to a plate and set aside.

Reduce the heat to medium and add the remaining 2 tablespoons of butter to the same skillet. Add the minced garlic and red pepper flakes if using, and cook for just 30 to 60 seconds, stirring constantly until fragrant. Watch closely to avoid burning the garlic, which can turn bitter.

Pour in the chicken broth to deglaze the pan, scraping up all those flavorful browned bits from the bottom with a wooden spoon. This adds incredible depth to your sauce.

Stir in the heavy cream and remaining Italian seasoning. Bring to a gentle simmer and let it cook for 2 to 3 minutes until the sauce coats the back of a spoon, stirring occasionally.

Reduce heat to low and gradually sprinkle in the freshly grated Parmesan cheese, stirring gently until it's completely melted and the sauce becomes velvety smooth. Be patient here as rushing can make the sauce grainy.

Add the seared chicken with any accumulated juices back into the skillet, followed by the drained pasta. Using tongs, gently toss everything together until the pasta and chicken are thoroughly coated in sauce.

If the sauce seems too thick, add small splashes of the reserved pasta water until you reach a silky, flowing consistency that clings to the pasta. Taste and adjust seasoning with additional salt and pepper if needed.

Serve immediately with a generous sprinkle of fresh parsley on top.