Set sous vide machine to 55C/131F.
Salt the shrimp to taste. Put the shrimp in a freezer bag, and remove the air through a vacuum sealer or the displacement method. Place in sous vide bath for 30 minutes.
Remove bag from bath. Take shrimp out of the bag, and lightly season with salt to taste. Set shrimp aside.
Heat a large pot of salted water until it is boiling. Add fettuccine and cook for 8-10 minutes, or al dente. Once pasta is cooked, drain water.
In a large skillet, add garlic and butter and cook for one minute. Pour in half-and-half and stir to mix ingredients. Slowly mix in Parmesan cheese one tablespoon at a time, stirring constantly. Once all Parmesan is added, salt to taste. Keep stirring sauce frequently to ensure it does not boil, until it is thickened.
Once alfredo sauce has thickened, add pasta and stir until fettuccine is coated with sauce evenly. Top pasta with shrimp, garnish with chopped parsley and enjoy!