In a large pot, bring salted water to a rolling boil. Carefully add the fettuccine and cook according to the package instructions, usually about 8-10 minutes, until the pasta is al dente. Drain the pasta and set aside, reserving a small cup of pasta water for later use if needed.
In a large skillet, heat the olive oil over medium heat. Add the sliced smoked sausage and sauté for about 5-7 minutes, until the sausage is nicely browned and heated through, stirring occasionally for even cooking.
Once the sausage is browned, add the finely chopped onion and minced garlic to the skillet. Sauté together for about 3-4 minutes, or until the onions become translucent and fragrant.
Sprinkle the Cajun seasoning evenly over the sausage and onions. Stir thoroughly to ensure the ingredients are well coated with the spices, enhancing the flavor profile.
Gradually pour in the heavy cream, stirring constantly as you bring the mixture to a gentle simmer. Allow it to cook for about 3-5 minutes, stirring occasionally, until the sauce begins to slightly thicken.
Reduce the heat to low and incorporate the grated Parmesan cheese into the sauce, stirring continuously until the cheese has completely melted and the sauce is velvety smooth. If the sauce becomes too thick, add a splash of the reserved pasta water until you reach the desired consistency.
Add the cooked fettuccine to the skillet, tossing gently to ensure the pasta is fully coated in the creamy Alfredo sauce. Taste and adjust seasonings with salt and pepper as necessary.
Just before serving, stir in the chopped parsley to add a fresh note to the dish.
Notes
Serve in deep bowls with extra Parmesan and parsley for garnish.