Bring a large pot of salted water to a boil and cook the 12 ounces pasta until al dente. Drain, reserving about a cup of the pasta water, and set aside.
While the pasta cooks, pat the 1½ pounds chicken breasts dry and season both sides with the 1 teaspoon Italian seasoning, 1 teaspoon smoked paprika, ½ teaspoon salt, and ½ teaspoon black pepper. Heat the 2 tablespoons olive oil in a large skillet over medium high heat and cook the chicken whole for 6 to 7 minutes per side, until golden and cooked through to 165°F (74°C). Transfer it to a cutting board to rest.
Lower the heat to medium and melt the 5 tablespoons butter in the same skillet. Add the 8 cloves minced garlic and cook for 1 minute, until fragrant but not browned, since burnt garlic turns bitter.
Sprinkle in the 3 tablespoons flour and stir for 1 minute, until it coats the garlic and loses its raw smell. This is what thickens the sauce into something rich and creamy.
Slowly pour in the 3 cups chicken broth while whisking to keep it smooth, then stir in the 2 cups heavy cream. Bring to a gentle simmer and cook for 4 to 5 minutes, until thickened enough to coat the back of a spoon.
Reduce the heat to low and stir in the 2 cups Parmesan, ½ teaspoon garlic powder, ½ teaspoon smoked paprika, and ¼ teaspoon red pepper flakes, a handful of cheese at a time, until melted and silky. Adding the cheese off the boil and in batches keeps the sauce smooth instead of grainy.
Add the drained pasta to the skillet and toss until coated in the sauce, keeping it saucy. If it thickens too much, loosen it with a splash of the reserved pasta water. There is plenty of sauce here on purpose, so you can spoon extra over and still have some to save.
Slice the rested chicken breasts and arrange them over the top of the pasta. Spoon extra sauce generously over the sliced chicken. Sprinkle with the 2 tablespoons parsley and serve right away, while it is hot and creamy.