Season the chicken breasts with Cajun seasoning and kosher salt on both sides. Heat a large skillet over medium-high heat and melt 2 tablespoons of unsalted butter. Once sizzling, add the chicken and sear for about 5-6 minutes on each side until it reaches 165°F. Remove from skillet and let rest.

Bring a large pot of salted water to a boil over high heat. Add fettuccine and cook for about 2-3 minutes less than package instructions for al dente. Reserve 1 cup of pasta water before draining and set aside.

In the same skillet, add the remaining 2 tablespoons of butter and 1 cup of chicken broth over medium heat. Once melted, add minced garlic and sauté for about 1 minute until fragrant.

Reduce heat to low, stir in 1 cup of heavy whipping cream, and gradually add grated Parmesan cheese, stirring until melted and thickened. Adjust seasoning if needed.

Add cooked fettuccine, reserved pasta water, and minced parsley to the sauce. Toss until pasta is evenly coated. Slice rested chicken and arrange on top of pasta. Garnish with extra parsley and serve.