Bring a large pot of salted water to a boil. Add the 8 ounces of fettuccine and cook according to package instructions until al dente, about 8 to 10 minutes. Stir occasionally to prevent sticking. Drain the pasta, reserving about 1/2 cup of pasta water.
In a large skillet over medium heat, melt the 1/2 cup unsalted butter. Once melted and gently bubbling, pour in the 1 cup heavy cream. Stir continuously and let simmer gently for 3 to 4 minutes until slightly thickened.
Sprinkle in 1 teaspoon garlic powder and stir to combine. Slowly add 1 cup grated Parmesan cheese a little at a time, stirring constantly until melted and smooth. Season with salt and freshly ground black pepper to taste.
Add the drained fettuccine to the skillet with the sauce. Toss gently to coat each noodle thoroughly. If the sauce is too thick, add a splash of the reserved pasta water to loosen it up.
If using cooked chicken or turkey, stir it into the pasta now to warm through for a heartier meal.
Transfer the Alfredo fettuccine to serving plates or a large bowl. Garnish with freshly chopped parsley and serve immediately while warm.
