01 - Bring a large pot of salted water to a boil. Cook fettuccine according to package instructions until al dente. Drain and set aside, reserving 1/2 cup pasta water.
02 - Pat chicken breasts dry with paper towels. Rub both sides thoroughly with Cajun seasoning, salt, and black pepper, pressing gently to adhere.
03 - Heat olive oil in a large skillet over medium-high heat. Add chicken and cook 5 to 6 minutes per side until blackened and cooked through, reaching an internal temperature of 165°F. Remove from pan, cover loosely with foil, and let rest 5 minutes before slicing thinly.
04 - In the same skillet, wipe out excess oil if needed. Melt butter over medium heat. Add minced garlic and sauté 1 minute until fragrant, being careful not to burn.
05 - Pour in heavy cream, stirring constantly. Bring to a gentle simmer, then add Parmesan cheese, black pepper, and salt. Stir until smooth and thickened, about 3 to 4 minutes. Add a splash of reserved pasta water if needed for desired sauce consistency.
06 - Add cooked fettuccine to the Alfredo sauce. Toss thoroughly with tongs until every strand is evenly coated.
07 - Divide pasta among serving plates. Arrange sliced blackened chicken on top. Sprinkle generously with fresh parsley and extra grated Parmesan.
08 - Serve immediately while hot. Pairs excellently with a crisp green salad and garlic bread, or with a dry white wine such as Sauvignon Blanc.