Cook fettuccine according to package directions until al dente. Drain, reserving 1 cup of pasta water.

While pasta cooks, pat seafood dry and season generously with Cajun seasoning. Heat 1 tbsp butter and olive oil in a large skillet over medium-high heat. Add shrimp and scallops and cook for 1-2 minutes per side until seared and cooked through. Remove from skillet and set aside.

In the same skillet, melt the remaining 1 tbsp of butter over medium heat. Add minced garlic and cook for 30 seconds until fragrant.

Pour in the chicken broth, scraping the bottom of the pan. Reduce heat to low, then slowly whisk in the heavy cream. Let it simmer gently for 2-3 minutes to thicken.

Gradually stir in the freshly grated Parmesan cheese until the sauce is smooth. Season with additional Cajun seasoning, salt, and pepper to taste.

Add the drained fettuccine and cooked seafood to the skillet with the sauce. Toss to combine. If the sauce is too thick, add a splash of reserved pasta water. Serve immediately, garnished with fresh parsley.