Bring a large pot of water to a boil and season generously with salt. Cook the fettuccine until al dente according to package instructions, then drain and set aside, reserving 1/2 cup of pasta water.

Pat the shrimp dry and season evenly with Cajun seasoning. Heat oil in a large skillet over medium-high heat and cook the shrimp for about 2 minutes per side until opaque and the internal temperature reaches 120°F, then remove and set aside.

Reduce the heat to medium and add butter to the same skillet, allowing it to melt before stirring in the minced garlic. Cook for 1–2 minutes until fragrant but not browned.

Whisk together the chicken broth and cornstarch, then pour into the skillet along with the heavy cream. Bring to a gentle simmer and stir in the grated Parmesan cheese, cooking for 3–5 minutes until the sauce thickens enough to coat the back of a spoon.

Add the cooked fettuccine directly into the sauce and toss thoroughly to coat, adding a splash of reserved pasta water if needed to loosen the sauce. Let it simmer together for 1–2 minutes so the pasta absorbs the flavor.

Top the creamy pasta with the cooked shrimp and finish with fresh parsley. Serve immediately while hot and silky smooth.