Bring a large pot of salted water to a boil. Add the fettuccine and cook according to package directions until al dente. Reserve about 1/2 cup of pasta water before draining.

While the pasta cooks, melt 2 tablespoons of butter in a large skillet over medium heat. Add the shrimp and cook for 2-3 minutes per side, until pink and cooked through. Remove the shrimp and set aside.

In the same skillet, melt the remaining 2 tablespoons of butter. Add the minced garlic and cook for about 30 seconds, until fragrant.

Stir in the heavy cream, Parmesan cheese, salt, and pepper. Bring to a simmer and cook for 2-3 minutes, or until the sauce has thickened slightly.

Add the cooked fettuccine to the skillet with the Alfredo sauce. Toss to coat the pasta evenly. If the sauce is too thick, add a little of the reserved pasta water until you reach your desired consistency.

Stir in the cooked shrimp. Toss gently to combine.

Serve immediately, garnished with fresh parsley, if desired.