Preheat a large skillet over medium-high heat. Season chicken breasts with Cajun seasoning and kosher salt. Melt 2 tablespoons of unsalted butter in the skillet, sear the chicken for 6–8 minutes on each side until it reaches 165°F. Let it rest after cooking.

Bring salted water to a boil in a pot, add fettuccine, and cook for 1–2 minutes less than package instructions for al dente. Reserve 1 cup of pasta water before draining.

In the same skillet, melt another 2 tablespoons of butter over medium heat, add minced garlic, and sauté for 30 seconds. Pour in chicken broth and let it simmer for 2–3 minutes.

Reduce heat, stir in heavy whipping cream, and gradually whisk in Parmesan cheese until melted. Adjust thickness with reserved pasta water if needed.

Toss cooked fettuccine into the Alfredo sauce, adding more reserved pasta water until the sauce clings to the noodles.

Slice rested Cajun chicken and place it on top of the fettuccine. Garnish with chopped parsley and extra Parmesan cheese. Serve hot.