Cook pasta according to package directions until al dente. Reserve 1 cup of the pasta water before draining. Set aside.
Season the shrimp lightly with salt, pepper, and 1 teaspoon of the Cajun seasoning.
Heat olive oil and 2 tablespoons of butter in a large skillet over medium-high heat. Add shrimp and cook for 1-2 minutes per side until pink. Remove shrimp from the skillet and set aside.
Reduce heat to medium. Add the remaining 2 tablespoons of butter to the skillet. Add onion, bell pepper, and celery. Cook until softened, about 5 minutes.
Add minced garlic, the remaining Cajun seasoning, and smoked paprika. Cook for 1 minute until fragrant.
Pour in the chicken broth, scraping up any browned bits from the bottom of the pan. Bring to a simmer.
Stir in the heavy cream and cayenne pepper. Let the sauce simmer gently for 3-4 minutes until it thickens slightly.
Reduce heat to low. Stir in the Parmesan cheese until the sauce is smooth and creamy. Taste and adjust salt and pepper if needed.
Add the cooked pasta and the cooked shrimp back into the skillet. Toss everything to coat evenly in the sauce. If the sauce is too thick, add reserved pasta water, one splash at a time, until the desired consistency is reached.
Stir in the fresh parsley. Serve immediately.
Notes
For an authentic Louisiana flavor, use a Cajun seasoning blend that includes thyme and oregano.
If you prefer a thicker sauce, simmer the cream mixture for an extra two minutes before adding the cheese.
Use high-quality, aged Parmesan cheese for the best melting and flavor in the sauce.