Boil the Pasta: Bring a large pot of generously salted water to a rolling boil. Add fettuccine and cook until al dente (usually 1 to 2 minutes less than package instructions). Reserve 1/2 cup of starchy pasta water, then drain pasta and set aside.

Season & Sear the Shrimp: Pat peeled shrimp thoroughly dry with paper towels. Toss with 1.5 tablespoons Cajun seasoning. Heat 2 tablespoons butter and 1 tablespoon olive oil in a large 12-inch skillet over medium-high heat until foaming. Add shrimp in a single layer and sear for 1.5 to 2 minutes per side until pink, opaque, and deeply caramelized. Transfer immediately to a warm plate to avoid overcooking.

Aromatize Garlic & Deglaze: In the same hot skillet, melt remaining 2 tablespoons butter over medium heat. Add minced garlic and sauté for 60 seconds until fragrant, scraping up flavorful browned Cajun bits from the bottom of the pan. Pour in chicken broth to deglaze and simmer for 2 minutes until slightly reduced.

Simmer the Cream Sauce: Pour in heavy whipping cream and diced tomatoes. Bring to a gentle simmer over medium-low heat for 3 to 4 minutes until the sauce begins to thicken and coat the back of a spoon.

Melt Cheese & Emulsify: Turn heat to low. Stir in grated Parmigiano-Reggiano cheese until completely melted and smooth. Stir in fresh lemon juice. If the sauce is too thick, splash in 2 to 3 tablespoons of reserved starchy pasta water.

Toss & Combine: Add the drained fettuccine and seared shrimp back into the skillet. Toss gently with tongs for 1 minute until every pasta ribbon is coated in velvety Cajun cream sauce.

Garnish & Serve Hot: Remove from heat. Garnish with chopped fresh parsley, extra shaved parmesan, and freshly cracked black pepper. Serve immediately with warm garlic bread!